• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.8
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• pp.767-772
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• 2009

Laser shock peening(LSP) is proving to be better surface treatment than conventional one such as shot peening. The LSP process has a compressive residual stress into a metal alloy and a significant improvement in fatigue life. Our research is focused on applying finite element method to the prediction of residual stress through the LSP processing in some LSP conditions such as pressure and spot size induced by laser. Two analysis methods are considered to calculating the compressive residual stress. But the explicit solution and the static one after partially explicit solving are almost same. In LSP, because of very high strain rate($10^6s^{-1}$), HEL(Hugoniot Elastic Limit) is the most important parameter in material behavior modeling. As the circular laser spot is considered, 2-D axisymmetric elements are used and the infinite elements are applied to boundaries for no reflection. The relations of material properties and the LSP are also important parts in this study.

• Journal of Ship and Ocean Technology
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• v.8 no.3
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• pp.18-25
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• 2004

Sound reception system is required to detect the sound and the quadrantal direction of the other ship's horn sound, to overcome the effects of enclosed wall for navigation space, functioning as a sound barrier. However, the realized systems can only provide quadrantal information of the other ship. This paper presents a new arrangement of microphones, having geometrically symmetric deployment with the same distances between sensors and the same angles between adjacent sensors with respect to the geometrical center. The sound pressures received at microphones are transformed into the related envelope signals by applying Hilbert transform. The time delays between microphones are estimated by the correlation functions between the derived envelope signals. This envelope base processing mitigates the noises related to the reflection by ship and sea surface. Then, the directional information is easily defined by using the estimated time delays. The suggested method is verified by the generated signals using boundary element method for a small ship model with sea surface wave. The estimated direction is quite similar to the true one and therefore the proposed approach can be used as an efficient sound reception system.

• Journal of KIISE:Software and Applications
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• v.26 no.10
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• pp.1143-1155
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• 1999

셀룰러 방식의 이동통신 시스템에서 전파의 유효신호 도달범위를 예측하기 위해서는 전파전파 모델을 이용한 예측기법이 주로 사용된다. 그러나, 전파과정에서 주변 지형지물에 의해 발생하는 전파손실은 매우 복잡한 비선형적인 특성을 가지며 수식으로는 정확한 표현이 불가능하다. 본 논문에서는 신경회로망의 함수 근사화 능력을 이용하여 전파손실 예측모델을 생성하는 방법을 제안한다. 즉, 전파손실을 송수신 안테나간의 거리, 송신안테나의 특성, 장애물 투과영향, 회절특성, 도로, 수면에 의한 영향 등과 같은 전파환경 변수들의 함수로 가정하고, 신경회로망 학습을 통하여 함수를 근사화한다. 전파환경 변수들이 신경회로망 입력으로 사용되기 위해서는 3차원 지형도와 벡터지도를 이용하여 전파의 반사, 회절, 산란 등의 물리적인 특성이 고려된 특징 추출을 통해 정량적인 수치들을 계산한다. 이와 같이 얻어진 훈련데이타를 이용한 신경회로망 학습을 통해 전파손실 모델을 완성한다. 이 모델을 이용하여 서울 도심 지역의 실제 서비스 환경에 대한 타 모델과의 비교실험결과를 통해 제안하는 모델의 우수성을 보인다.Abstract In cellular mobile communication systems, wave propagation models are used in most cases to predict cell coverage. The amount of propagation loss induced by the obstacles in the propagation path, however, is a highly non-linear function, which cannot be easily represented mathematically. In this paper, we introduce the method of producing propagation loss prediction models by function approximation using neural networks. In this method, we assume the propagation loss is a function of the relevant parameters such as the distance from the base station antenna, the specification of the transmitter antenna, obstacle profile, diffraction effect, road, and water effect. The values of these parameters are produced from the field measurement data, 3D digital terrain maps, and vector maps as its inputs by a feature extraction process, which takes into account the physical characteristics of electromagnetic waves such as reflection, diffraction and scattering. The values produced are used as the input to the neural network, which are then trained to become the propagation loss prediction model. In the experimental study, we obtain a considerable amount of improvement over COST-231 model in the prediction accuracy using this model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.3
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• pp.185-192
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• 1993

A numerical model has been used for the prediction of wave agitations in a harbor which are induced by the intrusion and transformation of incident waves. Based on linear wave theory a mild-slope equation has been used. A partial absorbing boundary condition has been used on solid boundary. Functional has been derived following Chen and Mei(l974)'s technique based on Hybrid Element Method which uses finite discretisation in the inner region and analytical solution of Helmholtz equation in the outer region. Final simultaneous equation has been solved using the Gaussian Elimination Method. Helmholtz natural period and second peak period of seiche in Donghae Harbor coincide very well with the results from numerical calculation. Computed amplification factors show good agreement, especially when the reflection coefficient on solid boundary is 0.99, with those of measurements.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.3
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• pp.139-148
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• 2000

In this paper, the interaction of oblique incident waves with a bottom-mounted and fluid-filled flexible membrane structure is investigated in the frame of linear hydro-elastic theory. The static shape of a membrane structure containing the fluid of a specific density is initially unknown and must be calculated before the hydrodynamic analysis. To solve hydrodynamic problem, the fluid domain is divided into the inner and outer region. The inner solution based on discrete membrane dynamic model and simple-source distribution over the entire fluid boundaries is matched to the outer solution ba~ed on an eigenfunction expansion method. The numerical results were compared to a series of Ohyama's experimental results. The measured reflection and tran¬smission coefficients reasonably follow the trend of predicted values. Using the computer program developed, the performance of a bottom-mounted and fluid-filled flexible membrane strocture is tested with various system parameters (membrane shape, internal pressure, density ratio) and wave characteristics (wave frequencies, incident wave angle). It is found that a bottom-mounted and fluid-filled flexible membrane structure can be an effel;tive wave barrier if properly designed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.7
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• pp.1505-1510
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• 2014

High-Pass (ETC ; Electronic Toll Collection) system is one of the basic elements, which adopts a wireless communication method using 5.8 GHz and can realize a part of ITS (Intelligent Traffic System). On the other hand, communication errors occur frequently in Hi-Pass system due to signal erros, multi-path reflection, and/or system-to-system interferences. To solve these problems, an EM (Electro-Magnetic) wave absorber can be used. To solve these Problems, we fabricated some samples in the different composition ratios of Carbon, Sendust, and CPE, and it was confirmed that the optimum composition ratio of Carbon : Sendust : CPE is 10 : 40 : 50 wt.%. The complex relative permittivity and complex relative permeability were derived by using the measured data. In addition, the optimum design parameters for the absorber were determined by simulation. Then the absorption abilities were calculated by changing the thickness of the EM wave absorbers. As a result, the optimum thickness of the developed EM wave absorber was 2.85 mm with absorption ability over 22.4 dB at 5.8 GHz. Futhermore, the EM wave absorber was fabricated based on the simulated and designed values. The measured values agreed well with the simulated ones. Therefore, it was clearly shown that the developed EM wave absorber in this paper is to be applied in actual situations.

• Geophysics and Geophysical Exploration
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• v.2 no.1
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• pp.8-16
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• 1999

In terms of high resolution, seismic reflection survey is by far the most significant geophysical method applied to define subsurface structure. In shallow seismic reflection survey, it is, however, difficult to obtain high resolution image due to both the wave attenuation in the unconsolidated layer and the existence of source-generated surface waves Therefore, when collecting data, it is imperative to select proper equipments and choose optimum field data acquisition parameters for acquiring high S/N data. In this survey, a small size hammer was used as a low energy source and 40-Hz vertical geophones were used as receivers. Trigger signal was obtained from the hammer starter attached in the aluminum plate and thus it was possible to control the source onset time for the vertical stack. During the field work, a modified standard CMP technique was introduced to achieve the many-fold CMP data effectively. Data processing was conducted by the 'Seismic Unix' which is mounted on PC with a Linux operating system. The main distinctions were the emphasis and detail placed on near-surface velocity analysis and the extra care exercised in muting.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.5
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• pp.1-6
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• 1997

An analysis method for the electromagnetic scattering of a tE polarized plane wave from a periodic strip grating over a grounded dielectric slab is consisered from the viewpoint of reflectio ngraing problem. The strip gratings showing bragg and off-bragg balzing phenomena at the frequency of 10GHz are designed, respectively. The strip grating structure is implemented using aluminum plate (hround conductor), paraffin(dielectric material ; .xi.$_{\gamma}$=2.24) and copper (strip conductor ; 0.08mm thickness). The experimental results (reflection power) for bragg as well as off-bragg blazing phenomenon have been compared with the theoretical results and fairly good agreements between theory and experiment have been observed.ed.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.615-620
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• 2002

Probability distribution of the sea surface slope is estimated using sun glitter images derived from visible radiometer on Geostationary Meteorological Satellite (GMS) and surface vector winds observed by spaceborne scatterometers. The brightness of the visible images is converted to the probability of wave surfaces which reflect the sunlight toward GMS in grids of 0.25 deg $\times$ 0.25 deg. Slope and azimuth angle required for the reflection of the sun's ray toward GMS are calculated for each grid from the geometry of GMS observation and location of the sun. The GMS images are then collocated with surface wind data observed by three scatterometers. Using the collocated data set of about 30 million points obtained in a period of 4 years from 1995 to 1999, probability distribution function of the surface slope is estimated as a function of wind speed and azimuth angle relative to the wind direction. Results are compared with those of Cox and Munk (1954a, b). Surface slope estimated by the present method shows narrower distribution and much less directivity relative to the wind direction than that reported by Cox and Munk. It is expected that their data were obtained under conditions of growing wind waves. In general, wind waves are not always developing, and slope distribution might differ from the results of Cox and Munk. Most of our data are obtained in the subtropical seas under clear-sky conditions. This difference of the conditions may be the reason for the difference of slope distribution.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.643-646
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• 2005

The gas hydrate exploration using seismic reflection data, the detection of BSR(Bottom Simulating Reflector) on the seismic section is the most important work flow because the BSR have been interpreted as being formed at the base of a gas hydrate zone. Usually, BSR has some dominant qualitative characteristics on seismic section i.e. Wavelet phase reversal compare to sea bottom signal, Parallel layer with sea bottom, Strong amplitude, Masking phenomenon above the BSR, Cross bedding with other geological layer. Even though a BSR can be selected on seismic section with these guidance, it is not enough to conform as being true BSR. Some other available methods for verifying the BSR with reliable analysis quantitatively i.e. Interval velocity analysis, AVO(Amplitude Variation with Offset)analysis etc. Usually, AVO analysis can be divided by three main parts. The first part is AVO analysis, the second is AVO modeling and the last is AVO inversion. AVO analysis is unique method for detecting the free gas zone on seismic section directly. Therefore it can be a kind of useful analysis method for discriminating true BSR, which might arise from an Possion ratio contrast between high velocity layer, partially hydrated sediment and low velocity layer, water saturated gas sediment. During the AVO interpretation, as the AVO response can be changed depend upon the water saturation ratio, it is confused to discriminate the AVO response of gas layer from dry layer. In that case, the AVO modeling is necessary to generate synthetic seismogram comparing with real data. It can be available to make conclusions from correspondence or lack of correspondence between the two seismograms. AVO inversion process is the method for driving a geological model by iterative operation that the result ing synthetic seismogram matches to real data seismogram wi thin some tolerance level. AVO inversion is a topic of current research and for now there is no general consensus on how the process should be done or even whether is valid for standard seismic data. Unfortunately, there are no well log data acquired from gas hydrate exploration area in Korea. Instead of that data, well log data and seismic data acquired from gas sand area located nearby the gas hydrate exploration area is used to AVO analysis, As the results of AVO modeling, type III AVO anomaly confirmed on the gas sand layer. The Castagna's equation constant value for estimating the S-wave velocity are evaluated as A=0.86190, B=-3845.14431 respectively and water saturation ratio is $50\%$. To calculate the reflection coefficient of synthetic seismogram, the Zoeppritz equation is used. For AVO inversion process, the dataset provided by Hampson-Rushell CO. is used.