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This paper explores the effects of adding different forms of bulbous bows onto catamaran hulls and assesses the implications on the seakeeping performance. There has been a large body of work that assess’ the effect of wave wake wash and recently studies have been undertaken to determine the effects of bulbous bows on reducing wave wake wash. However, not much research has been published on the effects of bulbous bows on the seakeeping performance of catamarans fitted with bulbous bows. This paper presents experimental results that will allow a ship designer to understand the effects of bulbous bows on heave, pitch and added resistance in waves. In conclusion it ranks the importance of different bulbous bows on the seakeeping performance.

This paper introduces a practical formula for added resistance in short waves. Particularly, the formulation introduced by Faltinsen et al. (1980) is modified to consider the three aspects: the finite draught of ships, the local steady velocity, and the shape above still-water-level (SWL). First, an additional term due to the finite draught of ships is derived by subtracting the integration of velocity square terms along the vertical control surface from the ships draught to the negative infinite. Second, a new local steady velocity is proposed, which includes the variation of sectional area. Third, the bow shape above SWL is considered by introducing the ratio of bluntness coefficients at the mean level of steady waves and SWL. The mean level of steady waves is approximately calculated based on the steady wave elevation of an advancing wedge-shaped body in calm water. The effect of each modification has been investigated and compared to experimental results and other empirical formulae of added resistance in short waves. Finally, a practical approach to combine the modified formula and the existing computation method for the added resistance in an overall wavelength range is presented.

An attempt was made to extend and further tune the existing formula for approximating the added resistance in head seas to cover a wider range of speed and to account the impact of loading conditions; a new parameter based on B/ T was introduced after conducting extensive parametric study to capture the influence of draft on the added resistance; the trim effect has also been investigated; Furthermore, the draft effect on the added resistance due to diffraction is further tuned and simplified. The derived formula uses only a few input, including only some ship dimensions to yield an estimation of the added resistance of ships in regular waves. Numerical results show that the added resistance of various ships in head seas at low speeds, as well as the added resistance of tankers in ballast condition and cruise ships, can be properly captured by the new formula. Hence, it meets the demand of fast examination of the minimum power; it can also be used in the early design stage of a ship for power estimation.

An experiment was carried out with a ship model for prediction of added resistance in waves in the Flume of the Department of Water Resources Engineering of BUET. The flume has the dimension of 21.34 m x 0.762 m x 0.762 m, with wave generation facility at one end and an absorber at the other end. The overall length, breadth and depth of the ship model are 1 m, 0.213 m and 0.083 m respectively. The experiment was carried out in waves at different wavelengths and heights as well as in calm water at different speeds. The added resistance was determined by subtracting calm water resistance from the total resistance obtained in waves applying constant speed approach. The added resistance so obtained was expressed in non-dimensional form. The experimental results were compared with the theoretical ones obtained for the same ship model applying computer programs developed for ship added resistance in waves.

Computational ship hydrodynamics has gained high popularity in shipbuilding industry in recent years because of its high efficiency and improved accuracy. Reliable performance prediction at design stage is essential for large structures, like ships, to ensure design conformance and buyer ‘s acceptance. Thus, shipbuilders are emphasizing and relying more and more on computational methods. This paper aims at providing a comparative study of added resistance and related motion prediction using a Reynolds averaged Navier -Stokes (RaNS) and potential flow (PF) based solver, for a very large crude career, KVLCC2. The used RaNS solver, SHIP Motion, solves overset structured mesh using finite volume method. The PF solver is a commercial solver named HydroSTAR that uses 3D panel method for simulation and prediction. The paper compares both the results and shows that the RaNS solver is better in predicting added resistance, however, in case of motion predicting, both show similar level of accuracy.

Ship added resistance is a steady force of the second order which depends on the ship motions and wave diffraction in short waves. To predict the impact of liquid motions inside the ship hull, a flooded tank in the midship area is generated and the ship response to regular waves is calculated. Currently available mathematical models and numerical tools are used to enable new insights into the sloshing effects of a relatively large free surface of flooded water inside the ship hull. The liquid inside the tank is first considered as a solid body in order to make a distinction between the hydrostatic and the hydrodynamic effect on global ship motions. Source formulation panel method is used and wave loads acting on the ship hull are determined using the near-field formulation. Based on the potential flow theory, the influence of sloshing on the ship motions and added resistance is evaluated to get an insight into this complex hydrodynamic problem. The calculated results are compared with the available experimental data from the literature.

The authors previously introduced a semi-empirical formula that enabled fast estimation of the added resistance of ships in head waves, and in this study the formula is further refined for easy use in engineering applications. It includes an alternative ship draft correction coefficient, which better accounts for the wave pressure decay with ship’s draft. In addition, it only uses the speed and main characteristics of the ship and wave environment as input, and has been simplified to the extent that it can be readily processed using a pocket calculator. Extensive validations are conducted for different ship types at low to moderate speeds in various typical irregular sea conditions, and encouraging results are obtained. This relevant and topical research lies within the framework of the recent IMO MEPC.232(65) (2013) EEDI guidelines for estimating the minimum powering of ships in adverse weather conditions, which specify for the use of simple methods in current Level 2 assessment within engineering applications.

For large ships, the likely sea states the ships that may encounter in their lifecycle are in the region of short length waves, compared to ships' length, where the diffraction component of the added resistance (AR) is predominant. In this paper, a multi-objective optimisation of the bow form of the standard ITTC KVLCC2 tanker was performed in terms of the AR, calm water resistance, total resistance and energy efficiency design index. The AR was estimated using semi-empirical formulas developed by the Ship Design Laboratory of NTUA. A parametric geometry model of ship's bow region and optimisation process were developed by use of the CAESES/Friendship-Framework. The conducted multi-objective optimisation procedure showed that the AR is strongly correlated to ship's waterplane area coefficient, moderately to ship's stem profile and weakly to the bow's flare angle. The optimised bow design resembles closely the LEADGE-bow hull concept, which is becoming very popular in recent full type ship new-buildings.

Given the indication of the IMO’s intent to the application of the EEDI and EEOI, the complete and precise total resistance of a ship and induced speed loss in wind and wave is primarily required. This paper proposed a practicable method to evaluate the total resistance in seaway. Besides the still water resistance, the added resistance due to waves is computed using panel method and the wind resistance is obtained using CFD with the verification of an open wind test and statistical formula. The speed loss is acquired in consideration of the matching of the hull, engine and propeller. A hull optimization method is consequently presented based on the proper resistance evaluation approach. The approach is validated available and the total resistance of a ship could be reduced after hull optimization.

This article describes the evaluation of the wave profile of submarine at surface condition and deck flooding which occurred by the wave making pattern at the bow. Movement of ships and submarines on the free surface of calm water creates the surface wave. Because of the difference in the bow shape and freeboard height, the wave making system in ships and submarines is different. Rounded or elliptical bow shape of submarines generates a high bow wave which causes deck and bow wetness. This is because of the fact that in submarines, this situation arises a small freeboard. In submarines, Deck wetness (because of deck flooding) is a very important subject that has some remarkable consequences, such as increase in resistance and added weigh. The focus of this article is on the added frictional resistance in the deck wetness condition. The bow wave profile, deck wetness and added resistance are studied in several Froude numbers by computational fluid dynamics method. This analysis is performed for a bare hull model at two different drafts by Flow Vision (V.2.3) software based on computational fluid dynamics method and solving the Reynolds-averaged Navier–Stokes equations.

The Energy Efficiency Design Index (EEDI) of a 120 m long general cargo vessel is calculated. Ship specific correction factors in the EEDI calculation guidelines from the International Maritime Organization (IMO) result in the attained EEDI of the ship studied being 22% lower than the ship's actual CO 2 emissions per transport work. Even with these correction factors, we find that the EEDI of the vessel studied would have exceeded the reference EEDI value if it had been equipped with a heavy fuel oil or marine gas/diesel oil engine instead of a natural gas engine. The EEDI in Beaufort 6 wind and waves, EEDI weather , is also calculated, using three different calculation methods for the added resistance due to waves. Issues with the methods suggested by IMO and the International Organization for Standardization (ISO) for calculating the added resistance due to waves are pointed out.

Both parametric roll and added resistance in head seas are hot topics in ship hydrodynamics. Parametric roll with half the encounter frequency is usually not taken into account in the calculation of added resistance in regular head seas. In order to study the correlation between parametric roll and added resistance, firstly, a formula of added resistance in regular head seas with parametric roll taken into account based on Maruo theory is developed to investigate the effect of parametric roll on added resistance in regular head seas. Secondly, partially restrained free running experiments with and without roll motions are carried out respectively to investigate the effects of parametric roll on added resistance in regular head seas. The results of experiments and simulations using the C11 containership show that added resistance is affected by parametric roll, and the results of experiments also show that heave and pitch motions are distinctly affected by parametric roll.

The importance of the sufficiently accurate prediction of the added resistance and powering of large ships in representative seaways is discussed. We introduce an updated empirical formula that may be used by engineers for the fast estimation of the added resistance of ships in waves and validate this formula for ships with LPP > 250 m operating in realistic sea conditions. The importance of the accurate prediction of added resistance of large ships is demonstrated by numerical and experimental studies on both full and fine hull forms. It is shown that for large ships sailing in representative seaways, properly quantifying the spectral contribution of the added resistance in the region of λ/LPP ≈ 0.1∼0.5 is of paramount importance and further studies are necessary to resolve this issue for large ships. This also leads to a critical discussion about the ITTC recommended experimental procedure, when assessing the overall seakeeping performance of large size ships in representative seaways.

해상에서 사고선박을 예인할 때 피예인선의 저항을 추정하는 것은 중요한 과정의 하나이다. 피예인선에는 선체 자체의기본 저항 외에 각종 부가저항이 있는데, 가장 큰 성분중의 하나로 파랑에 의한 부가저항을 들 수 있다. 본 논문에서는ISO 15016 표준의 이론해석 방법에 의해 사고 선박 예인시 파랑중 부가저항을 추정하는 알고리즘을 정립하고, 이를 전산 프로그램으로 구현하였다. 예제 선박의 계산 결과를 기존의 표준 결과와 비교하였고, 이 알고리즘과 전산 프로그램은 실제로 사고 선박의 저항과 이에 따른 예인력 추정시 사용하기에 적절한 것으로 판단되었다.Abstract − It is one of the important processes to predict the resistance of the towed ship when towing a disabledship on the sea. Besides the basic resistance of hull itself, there are various added resistance, especially the addedresistance due to waves can be considered one of the biggest component. In this paper, the algorithm which predictthe added resistance due to waves of a disabled ship by theoretical analysis method of ISO 15016 standard wasestablished, and realized as a computer program. The calculated result for an example ship was compared withexisting standard one, and it is considered that this algorithm and computer program are appropriate to use for pre-dicting the resistance and towing force of the disabled ship actually.Keywords: Added Resistance(부가저항), Towed Ship(피예인선 ), Wave(파랑), Wind Wave(풍파), Swell(너울)

In this paper we develop and explore various simple semi-empirical formulations for the fast, but satisfactory estimation of the added resistance of ships in head waves. Relevant research work is in the frame of recent IMO-MEPC.232(65) EEDI guidelines for the estimation of minimum powering of ships in adverse weather conditions calling for suitable level 1 methods. We consider the effect of main characteristics of ship׳s hull form, with best fitting of available experimental data for different types of hull forms. A proposed new semi-empirical formula is simplified to the extent that it can be readily calculated using as input merely the speed and main characteristics of the ship and of the wave environment. Extensive validations of the proposed simplified formula for various ship hulls in both regular and irregular waves were carried out and compared to other comparable methods and more complicated approaches to the determination of the added resistance in head waves.

유가의 상승에 의한 연료비 증가는 중소 여객선사의 재무 상황 을 악화시키는 원인 중의 하나로, 이를 개선하기 위하여 저항성능 에 우수한 경제적인 선형의 확보가 필요하다. 여객선의 경우 일반 적으로 어느 정도 높은 운항속도를 가지기 때문에 저항성능 개선 을 위한 선형설계에 있어 조파저항감소를 위한 선수선형설계가 필 요하다. 선수형상의 중요한 설계개념 중 하나인 선수 벌브의 경우, 선수 벌브와 선수 어깨에서 발생되는 파도들의 상쇄에 의한 조파 저항감소를 얻을 수 있다. 유럽을 중심으로 여객선에 대하여 진행 된 연구 결과들을 보면, 여객선에 거위목 벌브(gooseneck bulb)를 적용함으로 저항성능 개선을 통한 연료비의 감소가 가능함을 보여 주었다 (Heimann & Harries 2003; Maisonneuve, et al., 2003; Valdenazzi, et al., 2003; Heimann 2005; James, 2006; Dominic, 2007). 거위목 벌브의 개념은 조파저항감소를 위하여 일 반 벌브들과는 다르게 수선면 위로 벌브의 체적 중심을 올리고, 벌 브 체적 중심 뒤에서는 벌브의 폭이나 높이를 일반 벌브들에 비하 여 작게 하여 좀 더 유리한 파도상쇄효과를 얻기 위함이다. 따라서 이러한 거위목 벌브를 여객선에 적용하기 위한 연구들이 진행되었 다. Yu, et al. (2010)의 연구에서는 유럽에서 연구되어진 여객선 선형 (Heimann, 2005)를 대상으로 거위목 벌브의 최대 폭을 변화 시켜가며 자유수면 변화와 압력저항 변화를 확인하였다. 그 결과 벌브 폭이 감소할수록 발산파는 증가하였지만 비선형파가 감소하 여, 압력저항이 감소됨을 확인하였다. Yu, et al. (2014)의 연구에 서는 거위목 벌브의 최대 폭, 횡단면 형상 그리고 높이방향 중심위 치와 길이들을 변화시켜가며 연구를 수행하여, 거위목 벌브 설계 에 활용 가능한 벌브 선형요소들의 상관관계를 파악하고자 하였다. 이러한 기존 국내외 연구들은 정수 중에서 평가된 저항성능에 대한 연구결과들이다. 하지만 실제로 선박의 운항 시 파랑에 의 한 부가저항이 발생되는데, 부가저항은 선박에 따라 정수 중의 저항보다 15~30%가량 증가할 수 있다 (Seo, et al., 2013). 따 라서 정수 중에서의 저항성능 뿐 아니라 파랑 중에서의 부가저항 성능을 파악하는 것 또한 필요하다. pISSN:1225-1143, Vol. 52, No. 4, pp. 290-297, August 2015

In this study, experiments were performed using a model of a very large crude oil carrier (VLCC), which is a typical blunt ship, in a wave-making towing tank. The aim of the experiments was to determine the effect of added resistance in waves on the various operating conditions of a VLCC. An analysis of the results was conducted to determine the characteristics of resistance performance in waves. In addition, the characteristics of added resistance on a tanker were analyzed under irregular waves based upon the above result. The experimental results showed that added resistance was the highest around ?/L = 1.0, and the added resistance increased with the increase of the ship speed. Furthermore, under even keel conditions, the added resistance was higher than that under the trim changes, and the smallest added resistance was measured at the trim by the stern. Based on the experimental results, this study proposes effective operating conditions by analyzing the characteristics of the mean added resistance and the expected extreme response in irregular waves.

Unmanned Surface Vehicle (USV) has very complex forces and states when sailing at sea. While the optimization of USV via regression equations usually has a lower precision. Rapidity and seakeeping tests have been conducted based on a USV model of JUST. The rapidity test is mainly ship model resistance test and the seakeeping tests include wave added resistance test, hydrostatic pitching test, pitching and heaving test under the wave. Response surfaces fitting vectors of rough water resistance, pitching significant value, heaving significant value is established while using VC++ language to write second-order response surface fitting programs after dimensionless conversion of test data. Mathematical model of USV navigation performance synthetical optimization is proposed, including systems of rapidity, maneuverability and seakeeping. A layered parallel genetic algorithm (L-P-GA) optimization program is written in VC++ language, which can optimize a variety of conditions with different design speed and displacements. The results indicate that the optimization method has a higher precision and it can provide an opportunity to optimize the navigation performance of USV effectively.

It is critical to be able to estimate a ship׳s response to waves, since the resulting added resistance and loss of speed may cause delays or course alterations, with consequent financial repercussions. Slow steaming has recently become a popular approach for commercial vessels, as a way of reducing fuel consumption, and therefore operating costs, in the current economic and regulatory climate. Traditional methods for the study of ship motions are based on potential flow theory and cannot incorporate viscous effects. Fortunately, unsteady Reynolds-Averaged Navier–Stokes computations are capable of incorporating both viscous and rotational effects in the flow and free surface waves. The key objective of this study is to perform a fully nonlinear unsteady RANS simulation to predict the ship motions and added resistance of a full scale KRISO Container Ship model, and to estimate the increase in effective power and fuel consumption due to its operation in waves. The analyses are performed at design and slow steaming speeds, covering a range of regular head waves, using a commercial RANS solver. The results are validated against available experimental data and are found to be in good agreement with the experiments. Also, the results are compared to those from potential theory.

This study considered the uncertainty analysis in the measurement of the motion response and added resistance of waves in seafaring conditions. Methods of uncertainty analysis for seakeeping experiments are not well established. Particularly, no previous studies have specifically investigated added resistance measurements in seafaring conditions. In this study, uncertainty analysis based on ITTC Recommended Procedures and Guidelines (2008a), adopted with the method used by the International Organization for Standardization (ISO, 1995), was conducted and the assessment results are summarized in tabular form. The ship model used in the experiment is KVLCC2 ship, which has a hull shape of a typical large tanker. Vertical motion and added resistance were measured at nine regular waves in head sea. For the validation of the measured data, the experimental results were compared with not only those obtained at other test facilities but also the computational results found via strip and Rankine panel methods. In three cases among the nine wave conditions, at least 15 repeated measurements were conducted for the uncertainty analysis of the heave, pitch, and added resistance quantities. In this paper, the sources of uncertainty in added resistance measurement are summarized, and their uncertainties are quantified. From the uncertainty analysis, the sensitivity to each uncertainty source was observed. The present study will be useful in understanding the fundamental uncertainties associated with the towing tank measurement of motion responses and added resistance in waves.

Added resistance of ships in waves is determined by a newly developed potential flow method, a Rankine source method, a strip method, and by RANS (Reynolds-averaged Navier-Stokes) equations solvers. For 10 ships, results of all these methods are compared with each other, with published computed and experimental results, and with approximation formulae submitted to IMO (International Maritime Organisation). The focus is on waves that are short relative to ship length. In spite of the large scatter of results, existing prediction methods appear useful for practical application.

국제적으로 친환경에 대한 관심이 증가하고, 국제해사기구 (International Maritime Organization, IMO)가 선박의 온실가스 방출을 규제하기 위해서 2013년부터 선박연비제조지수 (Energy Efficiency Design Index, EEDI)를 도입하면서 조선 및 해운업계 에서는 선박의 운항 효율이 주요 관심사가 되었다. 선박의 운항 효율을 향상시키기 위한 많은 방법 중에 하나로 파랑 중 저항을 감소시키는 방법이 고려되고 있다. 부가저항이란 선박이 실제 해 상에서 운항하는 경우 바람이나 파랑에 의해 정수 중 저항보다 증가하는 저항을 말하며, 이러한 부가저항은 선박에 따라서 정수 중에서 운항하는 경우의 저항보다 15~30%까지 커지는 경우도 있다. 따라서 부가저항을 정확히 예측하고 이를 효과적으로 감소 시키고자 하는 연구들이 수행되고 있다. 본 논문에서는 최근 수행되었던 부가저항의 예측을 위한 수조 실험 및 수치계산 기법에 대한 연구들에 대하여 체계적으로 살펴 보고, 그 결과들을 비교하여 여러 기법들에 대한 검증과 장단점, 그리고 실선 적용에 대한 활용성 등을 다루고자 한다. 파랑 중 부가저항의 추정을 위해 실험 및 수치적 연구는 1970~1980년대에 많이 수행이 되었으나 한동안 주목을 받지 못 하다가 최근 그린쉽에 대한 관심이 고조되며 근래들어 여러 연구 들이 수행되고 있다. 부가저항의 초기 연구는 실험에 기반하여 진행되었다. 부가저항 실험은 1970년대부터 Series 60 선형 (Gerritsma & Beukelman, 1972; Storm-Tejsen, et al., 1973), S175 컨테이너선 모델 (Fujii & Takahashi, 1975; Nakamura & Naito, 1977), Wigley 모델 (Journee, 1992) 등에 대한 연구가 진행되었다. 최근 Kuroda, et al. (2011)은 컨테이너선 기본선형 을 기준으로 선수부의 형상을 다양하게 변화시켜가면서 이에 따 른 부가저항 변화를 살펴보았다. 또한, Lee, et al. (2013)도 최 pISSN:1225-1143, Vol. 51, No. 6, pp. 459-479, December 2014

Added resistance in waves is the second-order steady force dependant on the ship motions. It significantly affects ship operability and causes speed loss. Therefore the required power and fuel consumption of a ship advancing in a seaway increase. In this paper, additional fuel consumption is approximated in relation to the increased resistance, i.e. the difference between the ship resistance in calm water and resistance while operating in waves. Ship advancing in regular head waves with different speeds is examined. Calm water resistance is calculated according to the potential flow theory and ITTC 1957 model-ship correlation line. The added resistance in waves is calculated using three- dimensional boundary element method based on the potential flow theory. Motion induced resistance due to heave and pitch motions as well as reflection induced resistance are taken into account. Therefore, overall assessment of added resistance in regular waves is achieved through evaluation of the ship drift forces and quadratic transfer function. The so-called near-field formulation is used to determine wave loads acting on the ship hull. Evaluation of increased fuel consumption is made on the basis of estimated added resistance for different speeds and wave frequencies. Correlation of fuel consumption with various wave frequencies that the ship may encounter in its voyage is obtained.

It has been claimed that the use of a ducted propeller instead of an open propeller reduces the pitching motions of a ship, and the added resistance in waves. In addition, there is the potential benefit of smaller loss in propulsive efficiency when the propeller loading increases due to added resistance. Although little documentation for the validity of these claims is found, they look reasonable, since the duct has an effect similar to a passive foil, which is proven to reduce the vertical plane motions of high speed vehicles. This paper investigates the effect of a duct on the seakeeping of conventional ships. It is shown how the effect of the duct on the motions can be modelled by an equivalent flat foil. The effect of duct on motions and added resistance is investigated using linear strip theory. Results of model tests using a conventional 120 m single screw cargo vessel with a ducted and an open propeller are presented. The model test results confirm the findings from the numerical calculations, which is that the duct needs to be much larger than what is typical for such a ship in order to have a significant influence on the seakeeping performance.

In this study, uncertainty analysis based on ITTC(International Towing Tank Conference) Recommended Procedures is carried out in the towing-tank experiment for motion responses and added resistance. The experiment was conducted for KVLCC2 model in head sea condition. The heave, pitch and added resistance were measured in different wave conditions, and the measurement was repeated up to maximum 15 times in each wave condition in order to observe the uncertainty of measured data. The uncertainty analysis was carried out by adopting the ISO-GUM(International Organization for Standardization, Guide to the Expression of Uncertainty in Measurements) method recommended by ITTC. This paper describes the details about the analysis method, uncertainty and the measured uncertainty for each source. The uncertainty analysis results are summarized as a tabular form. To validate the accuracy of the present measurement, the experimental results are compared with the results of numerical computation and other experiment. From the present uncertainty analysis, the main sources of uncertainty are identified, which can be very useful to improve the accuracy for added resistance experiment.

The transportation by sea of compressed natural gas is a very recent subject, prompted by recent changes in the perspectives of a possible economic exploitation of relatively small quantities of this hydrocarbon, available as by-product of oil extraction in off-shore fields. An automatic and integrated preliminary design procedure has been established to generate and evaluate feasible technical solutions for a trade of this kind. A first trial application has been carried out for a specific case, for which various feasible solutions corresponding to fleets composed of a different number of equal ships are generated. In the procedure, a parent hull shape is adopted in order to evaluate, through systematic variations of the main dimensions, all the elements necessary to perform the classical steps of the design spiral (like weight evaluation, buoyancy, trim and stability checks and motion resistance prediction) accounting for the mutual interaction between the various items. When possible and necessary, parts of the procedure have been calibrated with data from existing ships, in order to ensure realism in the predictions. This has been done with reference e.g. to the evaluation of weight items and in particular to hull weight. On the other hand, when setting boundaries to the range of variation in the ship dimensions, care has been given not to constrain the investigation domain only to existing dimensional ratios, but to let the procedure explore a wider range of solutions. A particular feature of the procedure is to include in the evaluation process the seakeeping performances in terms of added resistance in waves. This aspect interacts with the other part of the design process and influences the final outcome in terms of performance of the solution. The main implications of accounting for the increase in motion resistance are the capability of evaluating the reduction in the average speed, the corresponding reduction in the annual cargo delivery and the increase in fuel consumption (all aspects evaluated in respect to nominal conditions). The procedure, accordingly, is able to provide, in addition to several technical output identifying the various solutions (such as main dimensions, weight, power installed, seakeeping performances), indicators of the performances of the fleet in terms of annual cargo delivery, CapEx and OpEx, that can be used to rank the various solutions.

In this paper, added resistances acting on a hull of non ballast water ship (NBS) in high waves is discussed. The non ballast water ships were developed at the laboratory of the authors at Osaka Prefecture University, Japan. In the present paper, the performances of three kinds of bow shapes developed for the NBS were theoretically and experimentally investigated to find the best one in high waves. In previous papers, an optimum bow shape for the NBS was developed in calm water and in moderated waves. For a 2 m model for experiments and computations, the wave height is 0.02 m. This means that the wave height is 15% of the draft of the ship in full load conditions. In this paper, added resistances in high waves up to 0.07 m for a 2 m model or 53% of the full load draft are investigated. In such high waves linear wave theories which have been used in the design stage of a ship for a long time may not work well anymore, and experiments are the only effective tool to predict the added resistance in high waves. With the computations for waves, the ship is in a fully captured condition because shorter waves, λ/Lpp

The main aim of this paper is to generate practical added resistance diagrams to be used for the prediction of the increases in the frictional resistance coefficients and effective powers of ships due to the use of a range of coating and biofouling conditions. For this reason, an in-house code was developed based on the boundary layer similarity law analysis. Roughness effects of a range of representative coating and fouling conditions on the frictional resistances of flat plates across a large number of ship lengths were then predicted. Hence, an extensive database of added frictional resistance coefficients was evaluated for varying ship lengths, ship speeds and fouling conditions. The added resistance diagrams were then presented from 10 m to 400 m ship lengths and from slow to high ship speeds for each surface condition. Added resistances and powering penalties of different types of ships including DTMB 5415, KCS, JBC and KVLCC2 were predicted using the generated diagrams.

Starting with the physics nature of ships added resistance in waves, this paper mainly expounds the research development and present state in this field from theoretical prediction, experimental study and frontier of the added resistance. It seems that CFD and 3-D Green function are more applicable for solving the added resistance problem than traditional methods.

†Dept. of Marine Science and Production, Kunsan National University, Kunsan 573-701, Korea* Dept. of Ship & Ocean System, Inha Technical College, Incheon 402-752, Korea** Marine Simulation Center, Korea Maritime University, Busan 606-791, KoreaAbstract : Since most merchant vessels are mainly influenced by the added resistance in an actual sea, they could be navigated more efficiently if this added resistance could be precisely predicted and then effectively reduced. In this paper, we have computed the effective horsepower based on the resistance performance in still water and then calculated the added resistance in regular wave in order to estimate a ship's propulsion performance on a voyage. Firstly, we have performed experiments using a model of KCS in a circulating water channel to estimate the flow characteristics around a container ship and the ship's resistance in still water. Then we have calculated the motion response function in regular wave as well as the values for the increase in resistance, and evaluated the ship's motion performance in waves according to the calculated response function. It was found that the resistance in waves increased because the ship's motion response value became larger as the ship's speed increased in the case of head sea. The effect of the added resistance could be reduced by maneuvering the ship to the encounter angle of 120° in areas of long wavelengths and to head sea in areas of short wavelengths. Key words :added resistance, still water, regular wave, motion response function, encounter angle, KCS †Corresponding author, smlee@kunsan.ac.kr 063)469-1814 * ucjeong@inhatc.ac.kr 032)870-2176** sun2hae@hhu.ac.kr 051)410-4765

In this paper, the effects of a foil attached to a ship on the ship motion, added resistance, and thrust generation in waves are analyzed. The unsteady theory for a two-dimensional foil is introduced to determine the coupled motion responses of the ship and foil. The thrust caused by the oscillating foil is evaluated and compared to the added resistance of the ship, so that a positive net thrust can be possible in waves. A comparison of the results of unsteady, quasi-steady, and experimental analyses is performed.

It is necessary to accurately evaluate the resistance performance and estimate the towing power of a tugboat for safety towing operation at actual seas. In this study, we have carried out the model tests firstly to investigate the resistance performance and flow characteristics around the tugboat in still water. The experiments are performed in infinite depth in circulation tank using 1/33.75 scaled model from 5kts to 10kts(designed speed 7kts) considering the effect of adverse and favorable current. Then the numerical calculations are executed to analyze the response amplitude operator and added resistance on tugboat due to the waves. The results obtained by the present computation are compared with the those acquired from the experiments in still water. As a result, it is noted that the added resistance become larger at head sea and higher speed conditions. We can also observe that the EHP increase 70 percent in comparison with those in still water.

In this study, numerical computation was carried out for evaluating the effects of the design parameter variations on the added resistance of Aframax tanker in head seas. The design of experiments (DOE) was used to efficiently conduct the numerical simulations with the hull form variations and save computational resources. A computational fluid dynamics (CFD) code based on the continuity and Reynolds averaged Navier-Stokes (RANS) equation was used for the numerical simulation. The simulation was performed in a short wave condition where the wave length was half of the ship length, which is expected to be most frequent in the vessel operation. Five design parameters of fore-body hull form were selected for the variations: design waterline length (DWL), bulbous bow height (BBH), bulbous bow volume (BBV), bow flare angle (BFA) and bow entrance angle (BEA). Each parameter had two levels in the variations, thus total 32 cases were designed initially. The results of the numerical simulations were analyzed statistically to determine the main effects and correlations in the five design parameters variations. Among them, the most significant parameter that influences on the added resistance in waves was DWL, followed by BBV and BEA. The other parameters had little effects on the added resistance in waves. By the computations, it was revealed that Extending DWL and decreasing BEA promoted the reflection of waves more toward the side than forward. In addition, there existed two-way interactions for the following two-factor combinations: DWL-BFA, DWL-BEA, DWL-BBV, BBH-BBV.

In the present study, the added resistance of a containership in parametric roll motion is investigated. The numerical simulation is carried out using a three dimensional Rankine panel method along with the weakly nonlinear formulation. The added resistance is evaluated by a near-field method, namely, the direct integration of the 2nd-order pressure on a body surface. To calculate the component resulting from the large-amplitude roll motion, the higher-order restoring and Froude-Krylov forces on wetted hull surfaces are taken into account. With or without parametric roll in regular waves, the components of added resistance classified with respect to integral terms are compared to figure out the important of each term. Through the investigation, the correlation between the added resistance and parametric roll is derived from coupling and decoupling the components of roll motion and vertical motions.

During transit, a drillship moonpool creates added resistance that can be more than 50% of the total resistance and hence significantly increase the fuel consumption. This paper reports a real case study for reducing moonpool added resistance by model tests and Computational Fluid Dynamics (CFD) simulations. Model test data show that, unlike conventional ships that experience nearly constant resistance, a drillship resistance presents largely fluctuating behaviour. In CFD validation, the physics based CFD best practices are applied for resistance predictions. The largely fluctuating resistance is well captured in simulations. It is found from flow visualizations of the large amount of CFD simulation results that the high moonpool induced added resistance is mainly attributed to the vortices shed from the moonpool front wall, which enter into the moonpool and impinge on the rear wall. The CFD predicted mean resistance are in good agreement with the model test data, within 3% difference for a wide range of speeds. The well validated CFD tool is applied to study the effects of moonpool dimensions on the added resistance. The results of parametric study reveal a design principle that smaller moonpool dimension results in smaller added resistance. Through comprehensive CFD parametric study, a universal design principle and CFD best practice are established for industry applications.

− One of the primary purposes of tugs is for the towing of other ships in salvage operations. In orderto conduct such a task safely, the tug should be capable of generating the appropriate towing forces. Thereforethe prediction of resistance against a towed ship during towing operation is a very important and essential pro-cedure. This paper studies the ship resistance calculation program to predict towing force. The calculation pro-gram consists of the functions that calculate basic hull resistance in calm water, added resistance due to wind,drifting, hull roughness, waves, shallow water and currents. All predictions are calculated by statistical andempirical methods by graph or formula. The calculation results made by this program are compared with theresults from the U.S. Navy’s Towing Manual. These results confirm that this computer program is quite capableof appropriately predicting the resistance of damaged ships.Keywords: Salvage(구난), Towing Force(예인력), Prediction(추정), Hull Resistance(선체저항), Addedresistance(부가저항 ), Speed Loss(선속 감소)

A reliable prediction of attainable ship speed at actual seas is essential from economical and environmental aspects. A methodology for estimating the attainable speed in moderate and severe sea is proposed. The irregular sea is handled as a series of regular waves with different amplitudes and frequencies. The added resistance in regular waves is obtained by either a direct pressure integration method or an asymptotic small wavelength formula. The in-and-out-of-water-effect and ventilation of a propeller in severe seas is accounted for by a quasi-steady averaging of experimental data for different propeller submergences. The propulsion results for regular waves are used in simulating results in irregular waves. It is shown that for higher sea states this effect has much more influence on the speed loss than the added resistance in waves. The speed loss is calculated by taking into account the engine and propeller performance in actual seas as well as the mass inertia of the ship. The attainable ship speed is obtained as time series. Correlation of speed loss with sea states allows predictions of propulsive performance in actual seas. The expected CO2 emission for a containership is estimated for the Northern route of North Atlantic.

This paper addresses prediction of ship motion and propulsion system behaviour to demonstrate the effect of waves in real sea states. For a 8000 t deadweight tanker, three different stem shapes are studied experimentally and numerically. Numerical simulations of speed loss were performed in time and frequency domain, generally agreeing well with experimental results. While a conventional bow with bulb and flare gave least calm water resistance, a bow without bulb and flare gave least total resistance in severe wave conditions.

The internal flows of moonpool usually causes huge added resistance on drillships, and those are very complex to analyze. Therefore, not only experimental approaches but also numerical simulations are required for better investigations when dealing with the hydrodynamic problems of moonpool. In the present research, numerical simulations are used to find out why the resistance increases by moonpool on a running drillship. That is, the three-dimensional numerical simulations and model tests are carried out to examine the characteristics of internal flow and added resistance by changing the section of the moonpool in both longitudinal and transverse directions. Finally, based on the present studies, an optimized shape of the moonpool is suggested, which effectively reduces added resistance, and that is confirmed with three-dimensional numerical simulations and model tests.

In the shipping industry, as well as in other industries, a reduction in the greenhouse gas emissions is expected to help to reduce global warming. Shipbuilding companies are now developing ship hull forms to reduce greenhouse gas emissions with an emphasis on the vessel performance in actual seas where winds and waves are part of this environment. In this paper the bow shapes above the waterline, which may affect the added resistance in waves, are focused upon since the ship motion and wave reflection at the bow contribute to the added resistance in waves that can be reduced by an improvement in the bow shapes above the waterline. The relationship between the bow shapes above the waterline and the added wave resistance is investigated through tank tests in waves with model ships with different bow shapes. From the results of the investigation, the influences of the bow shape on the powering and greenhouse gas emissions is evaluated.

Parametric rolling in irregular head seas is investigated using numerical simulation in the time domain in this paper. The effect of the change in speed due to added resistance on parametric rolling is taken into account. Three methods of calculating the added resistance in irregular head seas are applied to this problem, and then Pinkster’s method, which considers the time-varying added resistance in irregular head seas, is extended for further investigations in this paper. Furthermore, the Froude–Krylov component of restoring variation is estimated with coupling from heave and pitch motions, and the hydrodynamic effects are extrapolated nonlinearly with regards to roll angle. Finally, the “practical non-ergodicity” of parametric roll is investigated with a model experiment at zero forward speed and using the simulation, and the effect of added resistance is investigated with the simulation.

A formula based on Maruo’s theory is presented for the added resistance in regular head seas when parametric rolling occurs. Firstly, the velocity potential of the radiation waves due to parametric rolling, sway and yaw motions should be superposed on the conventional velocity potential. Secondly, the added resistance is averaged within the time duration that is double the encounter period. Thirdly, the stationary-phase method which is used in Maruo’s method is also used to obtain the formula of added resistance in waves with parametric rolling taken into account as well as viscous roll damping. Fourthly, source distribution based on Maruo and Ishii's and Maruo and Iwase’s works is used to calculate the added resistance. Finally, the effect of parametric rolling on added resistance in regular head seas mainly results from viscous roll damping and it becomes larger as the amplitude of parametric rolling becomes larger.

The present paper provides the results of an investigation on STEP (Spray Tearing Plate) for reducing the added resistance in waves.The research has been started to develop a device for suppressing spray; thin wave like a film that is generated around the bow above the waterline when a ship runs in waves. The effect of STEP is examined through tank tests with a model of 2500TEU container ship equipped with bolsters for anchors. The optimum shape of STEP reduces the added resistance in waves by 10% at designed speed under the condition of summer full load in short head waves of 3 meter height. The 3% reduction of CO2 emission is indicated by the tank test results and calculation for ship performance in head waves and winds of Beaufort scale 6.

In this paper, CFD simulation results for a tanker model are compared with experimental data over a range of wave conditions to verify a capability to predict the sea-keeping performance of practical hull forms. CFD simulations are conducted using WISDAM-X code which is capable of unsteady RANS calculations in arbitrary wave conditions. Comparisons are made of unsteady surface pressures, added resistance and ship motions in regular waves for cases of fully-loaded and ballast conditions of a large tanker model. It is shown that the simulation results agree fairly well with the experimental data, and that WISDAM-X code can predict sea-keeping performance of practical hull forms.

선박이 파랑중을 항행할 경우에는 정수중에 비하여 저항이 증가하기 때문에 예부선의 안정성 확보를 위해 예선의 예인마력과 예인삭의 절단하중 등을 산정할 때에 부선의 정수중 저항값 및 파랑중 저항값을 정확히 추정해야 안전한 예항업무를 이행할 수 있다. 현재 정부에서 제안하고 있는 방법에 의하면 부선의 전저항 산정시 마찰저항, 조파저항, 공기저항은 선체의 형상 및 예선의 속력 등을 고려하여 산정하지만 부가저항은 유의파고에 따라 일률적으로 적용하고 있다. 본 연구에서는 파랑중 부가저항 추정을 위해 수치계산을 실시하여 wigley 선형에 대한 기존의 실험 데이터와 상호 비교함으로서 본 계산법의 유효성을 검증하고, 검증된 수치계산법을 토대로 실무에서 많이 사용되고 있는 두개의 부선 모델을 대상으로 계산을 실행한 결과 부선의 부가저항은 파도와의 만남각에 따라 약 0.3∼1.1톤, 예인속력에 따라 약 0.4∼1.2톤, 선수형상에 따라 약 0.5∼1.1톤으로 차이가 발생함을 확인하였다. 【It is necessary to estimate more accurately the resistance of barge in still water and waves to compute the break load of towline and towing power for safety towing performance. The method proposed by government has calculated the total resistance of barge which is composed of frictional resistance, wave making resistance and air resistance considering the shape of hull and towing speed. However, the added resistance is equally applied with the significant wave height regardless of the type of vessels. In this study, we have carried out the numerical calculation to estimate the added resistance of wigley model in waves and compared with the experiment data to confirm the accuracy of the method. Then the computation was executed for the barge varying shape of the bow. As a result, added resistance of barge was differently occurred i.e. 0.3∼1.1 ton according to encounter angle, 0.4∼1.2 ton according to towing speed and 0.5∼1.1 ton according to shape of bow.】