• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.226-233
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• 2002

In the field of research of sea keeping quality, much development has been made in recent years using the method of calculation based on the strip theory. It is very important to investigate the hull response of a fishing vessel in waves to ensure the safe navigation and fishing operation in rough seas by preserving excellent sea keeping qualities. For this purpose, the author measured various responses of three fishing vessels in waves using real sea experimental measuring system and analyzed the experimental data The results obtained can be summarized as follow. 1. The amplitudes of pitching motion in the experiments appeared low values with more than one peak occasionally in following sea and quartering sea, and the band width of those was found to be wide relatively. 2. The amplitudes of rolling motion in the experiments appeared high values with only one peak in following sea and quartering sea regardless of ship's tonnage, and the band width of those was found to be narrow relatively. 3. The comparisions of theoretical results with those of experiments for the pitching motions and rolling motion in following sea and quartering sea show that the theoretical values are higher slightly than those of experiments in both directions and the period at which the peak appears in the calculations and the experiments has good agreement approximately 4. The calculated responses of two vessels under a assumed wave of 2.2m height and 5.0sec period showed that the response of pitching motion of ship-A are 2.2 times bigger than those of ship-C in following sea and quartering sea, and the response of rolling motion of ship-A is 4.2 times bigger than that of ship-C in quartering sea.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.4
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• pp.591-598
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• 2002

In the ship structural design, the material cost of hull weight and the overall cost of construction processes should be minimized considering safety and reliability. In the past, minimum weight design has been mainly focused on reducing material cost and increasing dead weight reflect the interests of a ship's owner. But, in the past experience, the minimum weight design has been inevitably lead to increasing the construction cost. Therefore, it is necessary that the designer of ship structure should consider both structural weight and construction cost. In this point of view, multi-objective optimization technique is proposed to design the ship structure in this study. According to the proposed algorithm, the results of optimization were compared to the structural design of actual VLCC(Very Large Crude Oil Carrier). Objective functions were weight cost and construction cost of VLCC, and ES(Evolution Strategies), one of the stochastic search methods, was used as an optimization solver. For the scantlings of members and the estimations of objectives, classification rule was adopted for the longitudinal members, and the direct calculation method, GSDM(Generalized Slope Deflection Method), lot the transverse members. To choose the most economical design point among the results of Pareto optimal set, RFR(Required Freight Rate) was evaluated for each Pareto point, and compared to actual ship.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.3
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• pp.9-20
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• 1989

It is important to enhance the safety of ship structures as much as possible in order to prevent the disastrous collapse of structures. In fact, the strength problem of structures is closely related with the safety problem of structures. Recently, the direct calculation method using a rational approach based on the first principle is implemented into the structural design process instead of adopting empirical approach based on the rules. The structural designer have shown increased concern with the problem of adequacy of conventional design method based on the safety factor since it does not fully take into account some degree of variability of the applied loads on and the strength of ship structures. To deal with the analysis of structures effectively, it is necessary to have three stages being equally treated. The first one is load analysis, second one response analysis, third one safety analysis. For marine structures, most of research effort has been however put into the first and second stages. The third stage is normally done by simple procedures. Hence, the various probabilistic methods are compared in order to establish the reliability analysis techniques for ship structures. As a result, the advanced level 2 method is selected as a most effective and accurate reliability method. The validity of this method is further demonstrated by comparing the results with the conventional method for the problem of the longitudinal strength of hull girder of Ro-Ro ship.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.1-10
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• 1997

Viscous flow around actual ship is calculated by an use of RANS equations. The propriety of this computing method, usefulness to hull form design and the scale effect which is the effect of viscous flow depending on the scale of ship model are investigated. Reynolds stress is modelled by using k-${\varepsilon}$ turbulence model and the law of wall is applied near the body. Body fitted coordinates are introduced for the treatment of the arbitrary 3-dimensional shape of the ship hull form. The transformed equations in the computational domain are numerically solved by an employment of FVM. In the calculation of pressure, SIMPLE method is adopted and the solution of the discretized equation is obtained by the line-by-line method with the use of TDMA The calculations of two ships, 4410 TEU container carrier and 50,000 DWT class bulk carrier, are performed at model and actual ship scale. The results are compared and discussed with the model test results which are viscous resistance, nominal wake distribution at propeller plane and limiting streamline on the hull surface. They describe the effect of stem form and the scale effect very well. In particular, the calculated nominal wake distribution and limiting streamline are agreed qualitatively with the experiments and the viscous resistance values are estimated within ${\pm}5%$ difference from the resistance tests.

• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.541-548
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• 2020

To overcome the disadvantage of hull mounted sonar, many countries operate dipping sonar system for helicopter. Although limited in performance, this system has the advantage of ensuring the survivability of the surface ship and improving the detection performance by adjusting the depth according to the ocean environment. In this paper, a method to calculate the optimal depth of the dipping sonar for helicopters is proposed by applying an optimization algorithm. In addition, in order to evaluate the performance of the sonar, the Sonar Performance Function (SPF) is defined to consider the ocean environment, the depth of the target and the depth of the dipping sonar. In order to reduce the calculation time, the optimal depth is calculated by applying Simulated Annealing (SA), one of the optimization algorithms. For the verification of accuracy, the optimal depth calculated by applying the optimization technique is compared with the calculation of the SPF. This paper also provides the results of calculation of optimal depth for ocean environment in the East sea.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.2
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• pp.27-38
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• 1997

This paper is concerned with the calculation of the wave resistance for SWATH ships based on a low order Rankine source panel method. Two types of free surface boundary conditions, Dawson type (double model approximation) and Kelvin type (free stream approximation) are used. For the free surface boundary calculation, an analytic differentiation is employed instead of implementing a finite difference scheme. Then, the radiation condition is satisfied by, so called, the panel shift method. The numerical results using the above two methods are compared with those using the thin ship/modified slender body approximation and also with the experimental results. The SWATH models considered are a single strut SWATH and a twin strut SWATH together with the variations of two demihull separation distance. In order to prove the validity of the program developed, the numerical calculations for a Wigley mono hull and Wigley twin hulls are compared with the available experimental results.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.2
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• pp.131-136
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• 2011

The furrow calculation and traffic measurement of sailing ship using computer vision are useful methods to prevent maritime accident by predicting the possibility of an accident occurrence in advance. In this paper, sailing ships are recognized using image erosion, differential operator and minimax value, which can be verified directly because the calculated coordinates are displayed on electronic navigation chart. The developed algorithm based on area information of this paper has the advantage which is compared to the conventional radar system focused on point information.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.5
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• pp.552-560
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• 2013

In this paper, an optimization algorithm for the block assembly accuracy control assessment is proposed with consideration for the current block assembly process and accuracy control procedure used in the shipbuilding site. The objective function of the proposed algorithm consists of root mean square error of the distances between design and measured data of the other control points with respect to a specific point of the whole control points. The control points are divided into two groups: points on the control line and the other points. The grouped data are used as criteria for determining the combination of 6 degrees of freedom in the registration process when constituting constraints and calculating objective function. The optimization algorithm is developed by using combination of the sampling method and the point to point relation based modified ICP algorithm which has an allowable error check procedure that makes sure that error between design and measured point is under allowable error. According to the results from the application of the proposed algorithm with the design and measured data of two blocks data which are verified and validated by an expert in the shipbuilding site, it implies that the choice of whole control points as target points for the accuracy calculation shows better results than that of the control points on the control line as target points for the accuracy of the calculation and the best optimized result can be acquired from the accuracy calculation with a fixed point on the control line as the reference point of the registration.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.594-600
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• 2022

When a large liquefied natural gas (LNG) carrier is anchored at a coastal terminal, calculations on mooring forces of mooring cables induced by environmental loads such as strong winds and currents are needed to secure mooring safety. The advantages and disadvantages of several existing mooring force calculation methods are compared and analyzed with their application conditions. Resultingly, mooring equipment guidelines of the Oil Companies International Marine Forum (OCIMF) are chosen as the computational method for this study. In this paper, the mooring forces of a large LNG carrier with spectrum was calculated using the OCIMF mooring equipment guidelines. The calculation shows similar maximum forces resulted from the calculation using experiment data of a wind tunnel test. To verify the results, OPTIMOOR, a dedicated mooring force calculation software, is used to calculate the same mooring conditions. The results of both calculations show that the computational method recommended by OCIMF is safe and reliable. OPTIMOOR calculates more detailed tensile force of each mooring cable. Thus, the calculation on mooring forces of mooring cables of a large LNG carrier using OCIMF mooring equipment guidelines is verified as an applicable and safe method.

• 한국기계연구소 소보
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• s.17
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• pp.133-144
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• 1987

Since the towing tank was operated from early 1979, the test and analysis methods have been established and applied for the performance prediction of ships. Especially the analysis programs for the resistance test ('EHP') and self-propulsion test ('DHP') based on the 1978 ITTC performance prediction method was modified as a name of 'PPTT' in order to include the form factor calculation, two-dimensional analysis method, the prediction on multi-screw ship and the organization of data filing system. Recently the program 'PPTT' was improved to cover the procedure of data fairing, the analysis of propeller-open-water test results carried out at low and high Reynolds numbers, etc. This paper describes the newly improved analysis program 'PTI'.