• 한국소음진동공학회논문집
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• 제13권9호
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• pp.679-687
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• 2003

Shock wave reduction in electrorheological(ER) smart structures is studied. ER insert is a composite structure comprising two elastic outer layers between which is sandwiched layer of ER fluid. When a voltage is applied across the outer layers. the shear modulus and the loss factor of the ER fluid are enabled, and thus the dynamic properties of the composite structure is altered. For the shock wave reduction in a hull mount of a submerged structure, ER inserts are made on the hull mount structure. To investigate the ER insert shape. many types of ER insert pattern are considered. Modal test of ER insert structures is performed to obtain the mode shapes, natural frequencies and the acceleration transmissibility. The acceleration transmissibility is reduced at such a frequency region when an electric field is applied. It is observed that the natural frequencies and mode shapes can be tunable by applying electric field. The ER-inserted hull mount is installed in an integrated system and the overall performance of shock wave reduction is tested. The possibility of shock wave reduction in the hull mount is demonstrated.

• 한국해안·해양공학회논문집
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• 제22권3호
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• pp.149-155
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• 2010

기존 월파량 산정식의 대부분은 파랑이 구조물에 직각으로 입사하는 조건에 대한 산정식으로서 경사입사파에 대한 연구는 미미한 실정이다. 또한 경사입사파 조건의 경우에도 상대적으로 짧은 모형을 실험에 적용함에 따라 경사입사파 내습시 구조물을 따라서 진행하는 파랑에 의한 월파를 고려할 수 없었으며, 단지 입사각에 따른 월파량 저감효과를 고려할 수 있는 월파량 저감계수(${\gamma}_{\beta}$)를 도입한 월파량 산정식을 제시하였다. 본 연구에서는 경사입사파 내습시 구조물 전면을 따라 진행하는 파에 의한 월파, 즉 월파의 공간적인 분포를 고려한 월파량 저감계수를 평면 수리실험을 통하여 제시하였다. 산정된 월파량 저감계수는 EurOtop(2007)에서 제시된 결과와 비교하였으며, 입사각이 $45^{\circ}$ 이상인 조건에 대해 EurOtop(2007)에서 제시한 월파량 저감계수를 개선하였다.

• 대한기계학회논문집B
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• 제21권9호
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• pp.1139-1148
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• 1997

Compression waves propagating in a high-speed railway tunnel develops large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations would cause an ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, experiments were carried out by using a shock tube with an open end. A blockage to model trains inside the tunnel was installed on the lower wall of shock tube, thus forming a sudden cross-sectional area reduction. The compression waves were obtained by the fast opening gate valve instead of a conventional diaphragm of shock tube and measured by the flush mounted pressure transducers with a high sensitivity. The experimental results were compared with the previous theoretical analyses. The results show that the ratio of the reflected to the incident compression wave at the sudden cross-sectional area reduction increases but the ratio of the passing to the incident compression wave decreases, as the incident compression wave becomes stronger. This experimental results are in good agreements with the previous theoretical ones. The maximum pressure gradient of the compression wave abruptly increases but the width of the wave front does not vary, as it passes over the sudden cross-sectional area reduction.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.872-877
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• 2005

The train entry into a tunnel generates a strong compression wave in the tunnel. The high amplitude of compression wave causes high pressure gradients that are responsible for both the aural discomfort of passengers and the impulsive acoustical wave called the miro-pressure wave. This paper provides a numerical study on effects of hood for micro'-'pressure wave reduction. An axisymmetric numerical solver, considering the cross sectional area of Korean Tilting Train eXpress, is used for a transient flow field in the tunnel. Results show that the micro-pressure wave is able to be reduced by a hood. In this results, the maximum reduction of micro--pressure wave is shown at 2L(length), 1.35D(diameter) hood around $56\%$ against the non-hood case.

• 한국해안·해양공학회논문집
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• 제29권2호
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• pp.121-127
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• 2017

구조물에 작용하는 실제 파랑은 다방향 불규칙파로써 장대 구조물의 경우 파의 위상차로 인해 파력의 감소효과가 발생한다. 본 연구에서는 이러한 효과가 파괴확률에 기여하는 정도를 파악하고 기존의 모듈형 방파제에 비해 어느 정도의 안정성이 확보되는지 확인하고자 기존 방파제 및 파력감소계수를 이용한 장대케이슨 방파제의 활동 파괴모드에 대해 신뢰성해석을 수행하였다. 그 결과 기존의 모듈형 케이슨 방파제보다 장대케이슨 방파제의 신뢰도지수가 더 높게 나타났고, 설계변수 중 유의파고가 가장 높은 영향을 미치는 것으로 확인되었다. 추가로 파력감소계수의 산정에 사용되는 변수들의 평균값 변화에 따른 신뢰성해석을 수행하였으며, 해석 결과 각 변수 값과 파력감소계수의 관계에서 확인된 경향이 평균값 변화에 따른 신뢰도지수 결과의 경향에 나타나는 것을 확인할 수 있었다.

• 한국해양공학회지
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• 제11권2호
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• pp.122-130
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• 1997

Coastal diaster induced by waves and countermeasures were investigated in the viewpoint of reduction of overtopping rate with enviroment in fishing port. The reduction method of wave overtopping rate using ecosystem control structures was proposed and studied on the efficiency by hydraulic and numerical experiments. The estimation models on wave overtopping rate was proposed after comparing previous models with dimensional analysis and experimental results. Control function o fwave overtopping by use of ecosystem controlstructures was simulated and discussed with combining wave shoaling-dissipation-breaking deformation model around ecosystem control structures and newly proposed calculation model for wave overtopping rate. Feasiblilty of ecosystem control structures could be confirmed for reduction of wave overtopping and fisheries-based multipurpose development of coastal zone.

• Journal of information and communication convergence engineering
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• 제15권3호
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• pp.175-181
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• 2017

This paper describes the upgrade of an existing wave information retrieval algorithm by employing noise reduction in the pixel domain. Several algorithms for collecting wave information parameters from X-band radar image sequences including the wind field and current velocity have been developed over the past three decades. Using these algorithms, a band-pass filter (BPF) is applied to remove the non-wave contribution from the image spectra after the sea surface current velocity has been computed. However, such BPF designs have been both complex and insufficient in removing undesired components in X-band radar images. For this study, to improve the performance of wave information retrieval, an efficient noise reduction algorithm is incorporated into a regular wave information retrieval process. That is, the proposed algorithm was designed for operation in a more proper manner by effectively removing the undesired components in the pixel domain. Experiment results demonstrate that the proposed algorithm produces very close estimates to the buoy data records under undesirable noise conditions.

• The Journal of the Acoustical Society of Korea
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• 제26권2E호
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• pp.50-55
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• 2007

SBN (Structure-Borne Noise) reduction in resiliently mounted machineries are predicted by using mass-spring model and wave model. In mass-spring model, mount is modeled as a spring, while in wave model, mount is considered as an equivalent elastic rod for taking account into longitudinal wave propagation. The predictions for SBN reduction through mounts are compared to the measurements for four different pumps. It is found that the mass-spring model is valid only in low frequency range below few hundred Hz, while for high frequency ranges longitudinal wave propagation in the mount must be considered to explain the measurements. It is also shown that impedance of the floor slightly affects low frequency behaviour in mass-spring and wave model below 50 Hz - 80 Hz, so that in engineering practice the effect of floor impedance may be neglected in computing mount performance.

• 한국해안·해양공학회논문집
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• 제28권1호
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• pp.1-6
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• 2016

수리실험을 통해 반파 구조물에 의한 월파 저감 효과를 정량적으로 분석하는 연구를 수행하였다. 원호 호안 및 경사 호안 모형에 대한 월파량을 계측하고 반파 구조물에 의한 월파량 저감 예측식과 비교하였다. 월파량이 비교적 많은 경우($q/{\sqrt{gH^3_s}}>10^{-3}$)에는 예측식과 실험 결과가 대체로 잘 일치하였으나, 월파량이 이보다 적은 경우에는 예측식과 실험의 편차가 크게 나타났다. 이러한 점을 고려하여 반파 구조물에 의한 월파 저감 효과를 보다 잘 예측할 수 있는 산정식을 개발할 필요가 있다.

• 한국생산제조학회지
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• 제19권2호
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• pp.198-203
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• 2010

In this paper, study on the mode characteristics analysis of the SH-EMAT (shear horizontal, electromagnetic acoustic transducer) waves for evaluating the thickness reduction in plates such as corrosion and friction is presented. Noncontact methods for ultrasonic wave generation and detection have been a great concern and highly demanded due to their capability of wave generation and reception on surface of high temperature or on rough surface. Mode identification of the SH-EMAT wave is carried out in an aluminum plate with thinning defects using time frequency analysis method such as wavelet transform, compared with theoretically calculated group velocity dispersion curve. The changes of various wave features such as the amplitude and the time-of-flight have been observed and the correlations with the thickness reduction have been investigated. Firstly, experiments have been conducted to confirm that it is possible to selectively generate and receive specific desired SH modes. These modes have then been analyzed to select the parameters that are sensitive to the thickness change. The results show that the mode cutoff and the time-of-flight changes are feasible as key parameters to evaluate the thickness reduction.