• Bulletin of the Society of Naval Architects of Korea
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• v.22 no.3
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• pp.9-18
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• 1985

The numerical calculation for solving boundary-value problem related to potential flows with a free surface is carried out by application of the localized finite element method. Only forced motion of 2-D body in infinitely deep fluid is considered, although this schemes is equally applicable to any first order time-harmonic problems of similar nature. The infinite domain of the fluid is separated into the inner flow field and the outer flow field with common inter-surface boundary. The finite element method is applied to obtain the solution in the inner flow field and the Green functions are utilized to represent the solution in the outer flow field. At the inter-surface boundary, the continuity of the value of potential and the normal derivative of the potential(i.e. matching condition) is conserved. The present method has better computational efficiency than the previous LFEM and the integral equation method of Frank. This enhanced computational efficiency is presumably due to the fact that the present method gives a symmetric coefficient matrix and requires less computational time in calculating the influence coefficient matrix of Green function than the integral equation method. And the irregular frequency desen't exist because the uniqueness of the solution is assured by the such that the exact free surface condition is satisfied on the boundary of the localized finite element region(i.e. inner region). As an example of the above method, the hydrodynamic forces for the circular cylinder and the rectangular cylinders are calculated. In the computed results, the small number of singularity distribution segments($3{\sim}6$) give good result relative to Ursell's and Vugts'.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.763-768
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• 2012

Active window system which can reduce the environmental noises, such as traffic noise and construction noise, from an open window into a room was proposed in the previous works. The key idea of the proposed active window system was that the control sources are approximately collocated with the primary noise source in terms of the acoustic power for global noise reduction throughout the interior room. Moreover, because it is important not to intrude into the living space in the building environment, no error sensors were used and an open-loop control method using control sources at the window frame and the reference sensors outside the room was used for the proposed system. The open-loop control gain was calculated by the interior room model assumed as the semi-infinite space, and the interior sound field was estimated by Rayleigh integral equation under the baffled window model assumption. However, windows with a finite thickness should were considered for the calculation of the open-loop control gain of the active window system since these are representative of most window cases. Therefore, the finite thickness window model based on the Sgard's model was derived and the open-loop control gain using the interior sound field estimated by that model was calculated for active window system. To compare the performance of these two models, a scale-model experiment was performed in an anechoic chamber according to noise source directions. Experimental results showed that the performance for the thickness window model is better than the baffled window model as the angle with respect to the perpendicular direction is larger.

• Journal of IKEEE
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• v.7 no.1 s.12
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• pp.32-42
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• 2003

In this paper, radiation pattern of rectangular microstrip patch antenna with anisotropy substrates and superstrate is studied by using a rigorous full-wave approach and a moment method calculation. Dyadic Green's function is derived for selected anisotropy material by constitutive relation. From these results, integral equations of electric fields are formulated. The electric field integral equations are discretized into the matrix form by applying Galerkin's moment method and then the current coefficients are obtained.. After solving the current coefficients, the far-zone electric field in spherical coordinates can be obtained by using the stationary phase method. To verify the validity of numerical result, we compare our result with existing one and get a good agreement between them. From the numerical results, the radiation patterns for variation of uniaxial superstrate thickness, anisotropy ratio of substrate and superstrate layer are presented and analyzed.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.4
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• pp.91-98
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• 1997

Most dynamic systems have various random properties m excitation and system parameters. In this paper, a procedure for structural response and reliability analysis is proposed for the linear dynamic system with random properties in both excitation and system parameters. The system parameter and response with random properties are modeled by the perturbation technique, and then the response analysis is formulated by probabilistic and vibration theories. Probabilistic FEM is also used for the calculation of mean response which is difficult by the proposed response model. The first passage analysis by the integral equation method is used to analyze the probability of failure. The integral equation method results in the first passage probability in terms of crossing rates and first passage probability densities. In this study it is assumed that excitations, system parameters and responses are Gaussian. As an application example, the probabilities of failure at transient state are calculated for a sdof system with random mass and spring constant subjected to stationary white-noise excitation and the results are compared to those of numerical simulation.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.713-724
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• 2004

A fatigue crack found at the coped stringer of the old dismantled Dangsan Subway Bridge was numerically simulated. A model of a single span of the plate girder bridge with its beam elements was created and analyzed in order to obtain the nominal stress history caused by trains. A detailed FEM analysis of the coped stringer was conducted using a shell element model. A fracture mechanical model was used to estimate crack propagation. The stress intensity factors were calculated using the J-Integral method. The simulation with some reasonable assumptions showed that the calculated crack lengths were comparable to those found on the site.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.2
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• pp.163-168
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• 2011

Robust optimization or reliability-based design optimization are some of the methodologies that are employed to take into account the uncertainties of a system at the design stage. For applying such methodologies to solve industrial problems, accurate and efficient methods for estimating statistical moments and failure probability are required, and further, the results of sensitivity analysis, which is needed for searching direction during the optimization process, should also be accurate. The aim of this study is to employ the function approximation moment method into the sensitivity analysis formulation, which is expressed as an integral form, to verify the accuracy of the sensitivity results, and to solve a typical problem of reliability-based design optimization. These results are compared with those of other moment methods, and the feasibility of the function approximation moment method is verified. The sensitivity analysis formula with integral form is the efficient formulation for evaluating sensitivity because any additional function calculation is not needed provided the failure probability or statistical moments are calculated.

• Nuclear Engineering and Technology
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• v.47 no.7
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• pp.791-803
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• 2015

The effective cross sections (XSs) in the direct whole core calculation code nTRACER are evaluated by the equivalence theory-based resonance-integral-table method using the WIMS-based library as an alternative to the subgroup method. The background XSs, as well as the Dancoff correction factors, were evaluated by the enhanced neutron-current method. A method, with pointwise microscopic XSs on a union-lethargy grid, was used for the generation of resonance-interference factors (RIFs) for mixed resonant absorbers. This method was modified by the intermediate-resonance approximation by replacing the potential XSs for the non-absorbing moderator nuclides with the background XSs and neglecting the resonance-elastic scattering. The resonance-escape probability was implemented to incorporate the energy self-shielding effect in the spectrum. The XSs were improved using the proposed method as compared to the narrow resonance infinite massbased method. The RIFs were improved by 1% in $^{235}U$, 7% in $^{239}Pu$, and >2% in $^{240}Pu$. To account for thermal feedback, a new feature was incorporated with the interpolation of pre-generated RIFs at the multigroup level and the results compared with the conventional resonance-interference model. This method provided adequate results in terms of XSs and k-eff. The results were verified first by the comparison of RIFs with the exact RIFs, and then comparing the XSs with the McCARD calculations for the homogeneous configurations, with burned fuel containing a mixture of resonant nuclides at different burnups and temperatures. The RIFs and XSs for the mixture showed good agreement, which verified the accuracy of the RIF evaluation using the proposed method. The method was then verified by comparing the XSs for the virtual environment for reactor applicationbenchmark pin-cell problem, as well as the heterogeneous pin cell containing burned fuel with McCARD. The method works well for homogeneous, as well as heterogeneous configurations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1167-1173
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• 2013

This study aimed to calculate the CFFs (critical flow functions) of a sonic nozzle bank with a 12-nozzle package within 1 s. Toward this end, the Helmholtz free energy of natural gas was formulated by using the AGA8-dc equation of state in a form without integral terms, and thereafter, thermodynamic properties such as the enthalpy, entropy, speed of sound, and heat capacity, which are used in CFF calculation, were derived in analytical form. As a result, the calculation time of CFFs was improved from 6.7 s in a previous study to 0.6 s per 12-nozzle package and kept almost constant regardless of the number of components in natural gas. Furthermore, it was confirmed that the calculated CFF values were in agreement with the results of a CFF international comparison test carried out under ISO management in 1998-1999.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.20 no.4
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• pp.383-388
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• 2002

This study suggests a data processing method for precise geoid height calculation through sea gravity data of mid-Yellow Sea provided by Haeyang 2000 and satellite altimetry data and the EGM96 geopotential model from GSFC/DMA in USA. Also it compared sea gravity data with satellite altimetry gravity data. As a result, precise geoidal undulation of the mid-Yellow Sea presented from calculating and integrating EGM96 geopotential model in degree and order 167 and a relative geoid by integral radius of 27km respectively It has a mean value of 18.339m, varying from 13.564m to 22.785m. the comparison between sea gravity data and satellite altimetry data shows that the former is more precise than the latter, which showed an anomaly of 0.56m0Gal and RMSE of 4.195m.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.1
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• pp.7-19
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• 1999

The energy transfer between sea-wave components by way of nonlinear wave-wave interactions plays a central role in spectral evolution. Since huge calculation time is required to exact computation of the resulting Boltzmann integral, however, the exact nonlinear energy transfer has not been directly introduced into operational wave models. Thus, effective calculation methods were examined in the present study which exploit the scale property of a scattering coefficient and the detailed balance of interactions. The improved Webb's method (IWM) has inherent stability because singularities degenerate into a negligible point. The improved Masuda's method (IMM) makes a quasi-analytical treatment of the inherent singularities and requires only 1.3 seconds of computer time via Pentium 300MHz processor. The IMM is, therefore, projected to be very useful for theoretical researches in spectral evolution with fetch- or duration-limited situations.