• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.135-142
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• 1998

In this study, the frequency transfer function of motions are predicted from the result of a full-scale seakeeping trials. Because the real sea has the characteristics of multi-directional waves,we compare the results in the one directional waves with ones in the directional waves. For calculation of the frequency transfer function in the directional waves, Takezawa's inverse estimation method was introduced and the frequency ranges were divided into three parts in order to consider following seas. The full-scale seakeeping trials was executed in the south sea of Korea using the stern trawler. Those results show that analysis method of the multi-directional waves is more reliable than that of one directional waves, and confirm the possibility of applying this method to the full-scale seakeeping trials.

• Wind and Structures
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• v.30 no.2
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• pp.141-153
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• 2020

Probabilistic information regarding directional extreme wind speeds is important for the precise estimation of the design wind loads on structures. A joint probability distribution model of directional extreme typhoon wind speeds is established using Monte Carlo simulation and empirical copula function to fully consider the correlations of extreme typhoon wind speeds among the different directions. With this model, a procedure for estimating directional extreme wind speeds for given return periods, which ensures that the overall risk is distributed uniformly by direction, is established. Taking 5 typhoon-prone cities in China as examples, the directional extreme typhoon wind speeds for given return periods estimated by the present method are compared with those estimated by the method proposed by Cook and Miller (1999). Two types of directional factors are obtained based on Cook and Miller (1999) and the UK standard's drafting committee (Standard B, 1997), and the directional risks for the given overall risks are discussed. The influences of the extreme wind speed correlations in the different directions and the simulated typhoon wind speed sample sizes on the estimated extreme wind speeds for a given return period are also discussed.

• Journal of Ocean Engineering and Technology
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• v.7 no.2
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• pp.114-120
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• 1993

Responses of marine vehicles and ocean structures in a seaway can be predicted by applying the probabilistic approach. When we consider a linear system, the responses in a random seaway can be evaluated through spectral analysis in the frequency domain. But when we treat nonlinear system in irregular waves, it is necessary to get time history of waves. In the previous study we introduced one-directional waves (long crested waves)as wave environment and carried out calculations and experiments in the waves. But the real sea in which marine vehicles and structures are operated has multi-directional waves (short crested waves). It is important to get a simulated random sea and analyse dynamic problems in the sea. We need entire sample function or probabillty density function to infer statistical value of random process. However if the process are ergodic process, we can get statistical values by analysis of one sample function. In this paper, we developed the simulation technique of multi-directional waves and proved that the time history given by this method keep ergodic characteristics by the statistical analysis.

• Environmental and Resource Economics Review
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• v.16 no.1
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• pp.171-197
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• 2007

In this paper we provide a methodology that permits test of feasibility of Porter hypothesis under limited data environment by utilizing two types of output distance function: Shephard distance function and directional distance function. The production technology supported by Porter hypothesis is embodied in the directional distance function. The average annual marginal abatement cost for $SO_2$ obtained by estimating the directional distance function is higher than the one obtained with the Shephard distance function by about 50 percent in the Korean electric power industry over the period 1970~1998. This result implies that feasibility of Porter hypothesis depends upon whether investment in production capital and process can bring more than a 50 percent increase in the average productivity.

• International Journal of Ocean System Engineering
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• v.2 no.4
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• pp.250-258
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• 2012

The distribution of wave heights is assumed to be a Rayleigh distribution, based on the assumption of a narrow band and Gaussian distribution of wave elevation. The present study was started with doubts about the narrow band assumption. We selected the wave spectra widely used to simulate irregular random waves. The wave spectra used in this study included the Pierson-Moskowitz spectrum, Bretschneider-Mitsuyasu spectrum, and JONSWAP spectrum. The directionality of the waves was considered. The cosine 2-l type directional spreading function and mixed form of the half-cosine 2-s type with Mitsuyasu type directional spreading are considered here to investigate the effects of a directional spreading function on random waves. The simulated wave height distribution is compared with a Rayleigh distribution.

• Journal of Korea Multimedia Society
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• v.7 no.12
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• pp.1639-1649
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• 2004

In this paper, a method for detection of forged signatures based on spectral analysis of directional gradient density function and a weighted fuzzy classifier is proposed. The well defined outline of an incoming signature image is extracted in a preprocessing stage which includes noise reduction, automatic thresholding, image restoration and erosion process. The directional gradient density function derived from extracted signature outline is highly related to the overall shape of signature image, and thus its frequency spectrum is used as a feature set. With this spectral feature set, having a property to be invariant in size, shift, and rotation, a weighted fuzzy classifier is evaluated for the verification of freehand and random forgeries. Experiments show that less than 5% averaged error rate can be achieved on a database of 500 signature samples.

• Journal of Ship and Ocean Technology
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• v.4 no.1
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• pp.28-36
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• 2000

Numerical simulation based on the superposition of ring waves generated by the linear periodic source distributions for the plunger type wave maker was accomplished. The characteristics of directional spreading function were investigated. Mirror images are also introduced to consider reflections of side-wall together with the reflection coefficient to account for the imperfect reflection from the real side wall in the long experimental towing tank. Unexpected spurious waves, resulting from the combined effect of finite breadth of segmented wave maker, wavelength and main wave maker, wavelength and main wave propagating direction, were observed in the line source method and also in the analysis of the directivity. The influence of spurious waves to the directional spreading function was also investigated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.344-347
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• 2000

We analyze the variation of coupling length as a function of the waveguide width for a directional coupler. It is interesting that the coupling length is not monotonic function of waveguide width for a given distance between the centers. The waveguide width for a maximum coupling length can be utilized for the optimum design of a directional coupler.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.10 no.3
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• pp.210-217
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• 2010

This paper presents integrated path planning and collision avoidance for an omni-directional mobile robot. In this scheme, the autonomous mobile robot finds the shortest path by the descendent gradient of a navigation function to reach a goal. In doing so, the robot based on the proposed approach attempts to overcome some of the typical problems that may pose to the conventional robot navigation. In particular, this paper presents a set of analysis for an omni-directional mobile robot to avoid trapped situations for two representative scenarios: 1) Ushaped deep narrow obstacle and 2) narrow passage problem between two obstacles. The proposed navigation scheme eliminates the nonfeasible area for the two cases by the help of the descendent gradient of the navigation function and the characteristics of an omni-directional mobile robot. The simulation results show that the proposed navigation scheme can effectively construct a path-planning system in the capability of reaching a goal and avoiding obstacles despite possible trapped situations under uncertain world knowledge.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.1
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• pp.1-7
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• 2004

GUI program for analyzing directional spectrum waves is introduced in this paper Basically, MLM (Maximum Likelihood Method) was used for this program which was additionally consisted of performing spectral and time domain analysis for two dimensional irregular waves. Moreover, the directionality of directional spectrum waves generated by single summation and double summation method was investigated based on MLM. The directionality from each summation method has good agreement compared with that of target wave spreading function in the case of single wide directional spectrum waves. In addition to this, the resolution of directionality in double summation method was investigated as introducing coherence function between each wave component