• Wind and Structures
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• 제38권4호
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• pp.261-275
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• 2024

Before performing an experimental study on the downburst-generated wave, it is necessary to examine the scale effects and corresponding corrections or compensations. Analysis of similarity is conducted to conclude the non-dimensional force ratios that account for the dynamic similarity in the interaction of downburst with wave between the prototype and the scale model, along with the corresponding scale factors. The fractional volume of fluid (VOF) method in association with the impinging jet model is employed to explore the characteristics of the downburst-generated wave numerically, and the validity of the proposed scaling method is verified. The study shows that the location of the maximum radial wind velocity in a downburst-wave field is a little higher than that identified in a downburst over the land, which might be attributed to the presence of the wave which changes the roughness of the underlying surface of the downburst. The impinging airflow would generate a concavity in the free surface of the water around the stagnation point of the downburst, with a diameter of about two times the jet diameter (D_jet). The maximum wave height appears at the location of 1.5D_jet from the stagnation point. Reynolds number has an insignificant influence on the scale effects, in accordance with the numerical investigation of the 30 scale models with the Reynolds number varying from 3.85 × 10⁴ to 7.30 × 10⁹. The ratio of the inertial force of air to the gravitational force of water, which is denoted by G, is found to be the most significant factor that would affect the interaction of downburst with wave. For the correction or compensation of the scale effects, fitting curves for the measures of the downburst-wave field (e.g., wind profile, significant wave height), along with the corresponding equations, are presented as a function of the parameter G.

• 동력기계공학회지
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• 제13권2호
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• pp.63-70
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• 2009

This paper discusses the influence on long-tenn predictions of the ship response in ocean by using the Global Wave Statistics data, GWS, and wave information from the remote sensing satellites. GWS's standard scatter diagrams of significant wave height and zero-crossing wave period are suggested to be corrected to a round number of 0.01/1000 fitted with a statistical analytic model of the conditional lognormal distribution for zero-crossing wave period. The GEOSAT satellite data are utilized which presented by I. R. Young and G. J. Holland (1996, named as GEOSAT data). At first, qualities of this data are investigated, and statistical characteristic trends are studied by means of applying known probability distribution functions. The wave height data of GEOSAT are compared to the data observed onboard merchant ships, the data observed by measure instrument installed on the ocean-going container ship and so on. To execute a long-tenn prediction of ship response, joint probability functions between wave height and wave period are introduced, therefore long-term statistical predictions are executed by using the functions.

• 한국해안해양공학회지
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• 제12권4호
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• pp.195-202
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• 2000

최근에 항내 정온도를 향상시키고 월파량을 저감시키기 위하여 구조물 내에 공극을 두어 파의 에너지를 감쇠시키는 방법이 널리 행해지고 있다. 본 연구에서는 소파구조물 중에서 슬릿케이슨, 이글루블록 및 중공블록을 선택하여 이들의 수리학적 성능을 비교·검토하기 위하여 수리모형실험을 수행하였다. 평상파 조건에서 소파효과는 슬릿케이슨이 가장 양호한 결과를 보여주며, 설계파 조건에서 월파량의 저감효과는 슬릿케이슨과 이글루블록은 비슷하나 중공블록은 다소 저감효과가 떨어지는 경향을 보여주고 있다.

• 한국해양공학회지
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• 제17권5호
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• pp.25-31
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• 2003

Numerical experiments have been conducted using the nonlinear combined refraction-diffraction model, in order to analyze the generation characteristics of stem wave, which is formed by the interaction between vertical structure and the oblique incident waves. The results of stem wave are discussed through the stem wave height distribution along/normal vertical structure, under the wide range of incident wave conditions-wave heights, periods, depths, and angles. Under the same wave height and period, the larger the incident wave angle, the higher the stem wave heights. According to the results of wave height distribution, in front of vertical structure, the maximum of stern wave heights occurs in the location bordering the vertical wall. Furthermore, the most significant result is that stem waves occur under the incident angles between $0^{\circ}\;and\;30^{\circ}$, and the stem wave height ratio has the maximum value, which is approximately 1.85 times the incident wave height when the incident wave angle becomes $23^{\circ}$.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.168-177
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• 2020

Many coastal engineering designs utilize empirical formulas containing the Equivalent Deep-water Wave Height (EDWH), which is normally given a priori. However, no studies have explicitly discussed a method for determining the EDWH and the resulting design wave heights (DEWH) under irregular wave conditions. Unfortunately, it has been the case in many design practices that the EDWH is incorrectly estimated by dividing the Shallow-water Wave Height (SWH) at the structural position with its corresponding shoaling coefficient of regular wave. The present study reexamines the relationship between the Shallow-water Wave Height (SWH) at the structural position and its corresponding EDWH. Then, a new procedure is proposed to facilitate the correct estimation of EDWH. In this procedure, the EDWH and DEWH are determined differently according to the wave propagation model used to estimate the SWH. For this, Goda's original method for nonlinear irregular wave deformation is extended to produce values for linear shoaling. Finally, exemplary calculations are performed to assess the possible errors caused by a misuse of the wave height calculation procedure. The relative errors with respect to the correct values could exceed 20%, potentially leading to a significant under-design of coastal or harbor structures in some cases.

• 한국해양환경ㆍ에너지학회지
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• 제14권2호
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• pp.138-145
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• 2011

이 논문에서는 Monte Carlo method를 이용하여 주어진 파랑스펙트럼에서 위상차를 임의의 수 (random number)를 발생시켜 파형의 시계열 자료를 시뮬레이션하여 freak wave의 발생 특성을 살펴보았다. 여러 가지 상태의 해상상태를 스펙트럼법에서 정의한 유의파고 $H_s$와 유의파첨도 $S_s$의 조합을 이용해서 표시하였다. 유의파첨도가 동일한 경우에는 $H_s$가 커질수록 freak wave 발생 확률이 낮아지며 $H_s$가 동일한 경우 유의파첨도가 커질수록 freak wave 발생확률이 높아진다. 주어진 해상상태에서 최대파고 $H_{max}$의 평균은 $S_s$의 값이 증가함에 따라 조금씩 증가한다. 그러나 freak wave의 평균파고는 $S_s$에 관계없이 일정한 값을 가지며 freak wave 파고의 평균은 $H_s$의 2배가 된다. $S_s$가 일정한 경우 $H_s$가 증가하면 파형의 평균 첨도(kurtosis)가 증가한다. 그러나 $H_s$가 일정한 경우 $S_s$가 증가하면 첨도의 평균은 감소한다. Freak wave 발생 기준인 이상지수(Abnormality index, AI)의 평균값은 $H_s$와 $S_s$에 관계없이 2.11 정도의 값을 가지며 AI의 최대값은 2.5-3.0 사이의 값을 가진다. 따라서 Linear focusing에 의해서 발생한 freak wave의 AI의 상한 값은 3.0 정도라고 추정할 수 있다.

• 한국해양공학회지
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• 제7권2호
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• pp.9-18
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• 1993

Numerical wave tank is a robust tool by which the nonlinear interactions between the body and the free-surface can be treated in time-domain. In this paper, a two-dimensional numerical wave tank based on the Spectral/Boundary-Element Method is developed, and applied successfully to the study of nonlinear wave diffraction around a submerged circular cylinder. Particularly, it is shown that the high-order wave components of significant wave height are developed in the lee-side of the cylinder and that these waves result in a negative drift force on the circular cylider.

• Journal of Mechanical Science and Technology
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• 제14권4호
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• pp.448-455
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• 2000

The bow wave breaking and the viscous interaction of stern wave are studied by simulating the free-surface flows. The Navier-Stokes equation is solved by a finite difference method in which the body-fitted coordinate system, the wall function and the triple-grid system are invoked. After validation, the calculations are extended to turbulent flows. The wave elevation at the Reynolds number of $10^4$ is much less than that at $10^6$ although the Froude number is the same. The numerical appearance of the sub-breaking waves is qualitatively supported by experimental observation. They are also applied to study the stern flow of S-103 for which extensive experimental data are available. Although the interaction between separation and the stern wave generation are not yet clear, the effects of the bow wave on the development of the boundary layer flows are concluded to be significant.

• 한국해양공학회지
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• 제34권1호
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• pp.26-36
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• 2020

An extreme value analysis of metocean data which include wave, wind, and current data is a prerequisite for the operation and survival of offshore structures. The purpose of this study was to provide information about the return wave, wind, and current values for the Barents Sea using extreme value analysis. Hindcast datasets of the Global Reanalysis of Ocean Waves 2012 (GROW2012) for a waves, winds and currents were obtained from the Oceanweather Inc. The Gumbel distribution, 2 and 3 parameters Weibull distributions and log-normal distribution were used for the extreme value analysis. The least square method was used to estimate the parameters for the extreme value distribution. The return values, including the significant wave height, spectral peak wave period, wind speed and current speed at surface, were calculated and it will be utilized to design offshore structures to be operated in the Barents Sea.

• 농업과학연구
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• 제47권3호
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• pp.553-565
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• 2020

This study did an empirical analysis using consumer survey data to determine whether Taiwanese consumers' preference for the Korean Wave affects their preference for Korean dried persimmons. There were 158 effective respondents used for the analysis, and the effects of the Korean Wave was estimated using ordered logit regression. The main results of this study were as follows. First, females more preferred Korean dried persimmons compared to men. Second, it was found that the housewife variable had a statistically significant positive effect at a significance level of 1% indicating that the degree of preference for Korean dried persimmons was higher compared to other occupations. Third, when the main place for purchasing dried persimmons was a department store or a large discount store, the analysis result showed a positive effect at a significance level of 1%. Finally, the Korean wave effect was found to have a statistically significant positive influence at a 1% significance level. In particular, it is worth noting that as the Taiwanese consumers' preference for the Korean Wave increased, the preference for Korean dried persimmons increased, which could be useful information for companies wishing to export Korean dried persimmon products to Taiwan. As a promotional plan for revitalizing Korean dried persimmons in Taiwan, conducting promotional events in conjunction with the Korean Wave, such as K-pop contests, and promoting persimmons that reflect Korean traditional culture should be considered.