• Journal of the Korean Society for Marine Environment & Energy
• /
• v.15 no.3
• /
• pp.177-185
• /
• 2012

Wave field measurements were made over a period of 18 days to study the spatial distribution of incident wave on seaweed tarm field around Gumil-up Sea, Wando, Korea. These measured data were compared with data from the Geomun-do ocean weather/wave observation buoy. A numerical simulation model that combined the offshore design wave with the seasonal normal incoming wave was used to study the incident wave distribution surrounding a seaweed farm. The results are summarized as follows. (1) On-site wave measurements showed that the major relationship between maximum and significant wave height was $H_{max}=1.6H_{1/3}$. (2) Offshore incident wave energy reaching the coast was greatly influenced by the wind direction. A north wind reduced the incident wave energy and a south wind increased it. (3) The calculated maximum wave height under the design wave boundany conditions was in the range of 4~5 m and the reduction in the incident wave height ratio ranged from approximately 38.1% to 47.6% at Gumil-up Sea. Under normal wave conditions, the maximum wave heights were 3.6~4.0 m in summer and 2.3~2.7 m in winter while the reduction in the incident wave height ratio was about 41.8% to 49.1%. (4) The sea state in the southern area of Gumil-up was the most affected by ocean waves, whereas the sea state in the northern area was very stable. The significant wave ratio in the south was about six times that in the north.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2001.10a
• /
• pp.108-116
• /
• 2001

In this paper, statistical properties of waves in the sea area of Mara-do, Korea are examined based on 1998-1999's wave data from a directional wave buoy which is located in Mara-do. Wave data aquisition rate, monthly maximium, minimum and mean wave heights, frequency of wave direction are summarized. Wave height and period scatter diagrams and n-year return period wave heights are estimated. Wave periods of maximum wave heights are also estimated.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.10a
• /
• pp.309-316
• /
• 2003

In this paper, The statistical properties of ocean waves in the sea area of Hong-do, Korea are examined based on 1998-2002's wave data from a directional wave buoy. Wave data aquisition rate, mean wave heights, frequency of wave direction are summarized. Wave height and period scatter diagrams and n-years return period wave heights are estimated. Wave periods of maximum wave heights are also estimated. Large amplitude wave characteristics during the typhoon Prapiroon in 2000, Rusa in 2002 are also examined.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.10 no.4
• /
• pp.204-210
• /
• 1998

This paper presents the development of the probability density function applicable for wave heights (peak-to-trough excursions) in finite water depth including shallow water depth. The probability distribution applicable to wave heights of a non-Gaussian random process is derived based on the concept of the maximum entropy method. When wave heights are limited by breaking wave heights (or water depth) and only first and second moments of wave heights are given, the probability density function developed is closed form and expressed in terms of wave parameters such as $H_m$(mean wave height), $H_{rms}$(root-mean-square wave height), $H_b$(breaking wave height). When higher than third moment of wave heights are given, it is necessary to solve the system of nonlinear integral equations numerically using Newton-Raphson method to obtain the parameters of probability density function which is maximizing the entropy function. The probability density function thusly derived agrees very well with the histogram of wave heights in finite water depth obtained during storm. The probability density function of wave heights developed using maximum entropy method appears to be useful in estimating extreme values and statistical properties of wave heights for the design of coastal structures.

• Journal of Navigation and Port Research
• /
• v.31 no.6
• /
• pp.471-478
• /
• 2007

This study is carried out the investigation of nonlinear characteristics of the field wave observation data acquired in the western sea area in Jeju island during one year. It is aimed to offer the fundamental data for Freak wave forecasting in real sea. For this, the nonlinear parameters of ocean waves, which are Skewness, Atiltness, Kurtosis and Spectrum band width parameter et al., are introduced, and the parameters are compared and discussed with some characteristics wave components, ie, significant wave height, maximum wave height, and so on. As a results, we know that the parameters describe nonlinear characteristics of observed wave spectrum broadly, are feebly related with occurrence of abnormal maximum wave height, namely freak event, however the Kurtosis, $K_t$ which is a degree of peakness of mode of surface elevation distribution, has better relationship than others.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.22 no.2
• /
• pp.120-125
• /
• 2010

A Monte-Carlo simulation method is proposed which can take uncertainties of scale and location parameters of Gumbel distribution into account straightforwardly in evaluating significant design wave heights with respect to return periods. The uncertainties of design wave heights may directly depend on the amounts of uncertainties of scale parameter and those distributions may be followed by Gumbel distribution. In case of that the expected values of maximum significant wave height during lifetime of structures are considered to be the design wave heights, more uncertainties are happened than in those evaluated according to return periods with encounter probability concepts. In addition, reliability analyses on the armor units are carried out to investigate into the effects of the uncertainties of design wave heights on the probability of failure. The failure probabilities of armor units to 5% damage level for 50 return periods are evaluated and compared according to the methods of taking uncertainties of design wave heights into account. It is found that the probabilities of failure may be distributed into wide ranges of bounds when the uncertainties of design wave heights are assumed to be same as those of annual maximum significant wave heights.

• Journal of Ocean Engineering and Technology
• /
• v.33 no.3
• /
• pp.252-258
• /
• 2019

In this paper, the time history of the surface elevation measured at the Draupner platform in the North Sea in 1995 is used to examine the statistical characteristics of the wave data. The wave statistics for 48 surface measurements, which contain three freak wave occurrences, are summarized. The quartiles, boxplots, correlations, and pair plots of 15 variables, along with the abnormality index, are presented. The kurtosis and skewness of the surface elevation are two variables that are highly correlated with the abnormality index, which defines freak waves. Principal coordinate analysis showed that the direction of the changes in the abnormality index agreed with the changes in the kurtosis and skewness. In addition, various wave heights, except the maximum wave height, showed a similar direction for the height changes, and various wave periods showed a similar direction for the period changes. Based on the correlations and PCA analysis, the kurtosis and skewness of the surface profiles are the two most important variables to predict the abnormality index.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.6 no.1
• /
• pp.88-93
• /
• 1994

This study is concerned with an analytic derivation of the probability density function applicable for wave heights in finite water depth using two different methods. As the first method of the study, a probability density function is developed by applying a series of polynomials which is orthogonal with respect to Rayleigh probability density function. The newly derived probability density function is compared with the histogram constructed from wave data obtained in finite water depth which indicate strong non-Gaussian characteristics. Although the probability density represents the histogram very well. it has negative density at large values. Although the magnitude of the negative density is small. it negates the use of the distribution function fer estimating extreme values. As the second method of the study, a probability density function of wave height is developed by applying the maximum entropy method. The probability density function thusly derived agrees very well with the wave height distribution in shallow water, and appears to be useful in estimating extreme values and statistical properties of wave heights in finite water depth. However, a functional relationship between the probability distribution and the non-Gaussian characteristics of the data cannot be obtained by applying the maximum entropy method.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.14 no.2
• /
• pp.138-145
• /
• 2011

In this paper time series wave data are simulated by the Monte Calo method using random numbers to generate random phases of the wave signal. The simulated wave signasl are used to study the characteristics of freak waves. Various sea states are represented by combinations of the significant wave height $H_s$ defined in the spectrum method and the significant wave steepness $S_s$. For a fixed value of $S_s$, the probability of the occurrence of the freak wave is decreased as $H_s$ increases. For a fixed value of $H_s$ the probability of the occurrence of the freak wave increases as $S_s$ increases. The average value of the maximum wave height increase as $S_s$ increases, but the average height of freak wave remains the same and the value approaches two times of $H_s$. For the fixed value of $S_s$, average kurtosis of wave elevation increases as $H_s$ increases, but for a fixed $H_s$, the average kurtosis decreases as $S_s$ increases. The average of abnormality index(AI) is around 2.11 irregardless of $H_s$ and $S_s$. The maximum value of AI lies between 2.5 - 3.0. Therefore it is conjectured that AI maximum due to linear focusing is 3.0.

• Korean Journal of Materials Research
• /
• v.14 no.12
• /
• pp.870-875
• /
• 2004

Heat flow characteristics in the newly developed Wave Heat Sink were analyzed under natural and forced convections by Icepak program using the finite volume method. Temperature distribution and thermal resistance of Wave Heat Sink with/without air vent hole on the top of fin were compared with those of a commercial Al extruded heat sink(Intel Heat Sink). Under the natural convection, the maximum temperature was $45.1^{\circ}C$ in the air vent hole typed Wave Heat Sink, which was superior to that of Intel Heat Sink. The thermal resistance was $2.51^{\circ}C/W$ in the air vent hole typed Wave Heat Sink, and it changed to $2.65^{\circ}C/W\;and\;2.16^{\circ}C/W$ with changes of gravity direction and fin height, respectively. Under the forced convection, the maximum temperature became lower than that under the natural convection. In addition, the thermal resistance lowered in the air vent hole typed Wave Heat Sink with higher fin height and it decreased with increasing the air flux.