• 대한조선학회지
• /
• 제5권2호
• /
• pp.27-33
• /
• 1968

The resistance decreasing effects of a bulbous bow have been investigated with the model test results of the Korean standard type 10,000GT cargo vessel equipped with several different sized bulbous bows. The best bulbous bow for the design is 3.66% bulb which decrease the residual resitance 5%. The new hull combined with a bulbous bow have to be designed in other to get more effects.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제13권1호
• /
• pp.858-876
• /
• 2021

Although widely used, the design of the bulbous bow for ships has been difficult due to the complex interference between the wave system generated by the bulb and the wave system of the ship hull. Until now, a bulbous bow has been often designed using Kracht charts, which were established based on model test data, but these charts apply only to ships with a block coefficient C_B = 0.56-0.82, Froude number Fn = 0.20-0.40, and the obtained bulb sizes are only close to optimal. This paper presents a new method for the optimal design of bulbous bow, starting from the design of an initial bulb using Kracht charts for ships with any block coefficient or Froude number, then resizing this initial bulb to define the optimal bulb sizes based on a multi-objective function of the required power reduction, and a combined solution of Computation Fluid Dynamics (CFD) analysis and surrogate models. This study was applied to a fishing vessel FAO 75, which has been model tested and used to design steel fishing vessels in Vietnam recently. The obtained quantitative results showed the same trend as the theory and practice, with a reduction of the ship's required power by about 14%.

• 대한조선학회논문집
• /
• 제31권1호
• /
• pp.50-62
• /
• 1994

본 논문에서는 비대선형에서 구상선수의 형상변화가 저항성능에 미치는 영향을 조사해 보기 위하여 구상선수 계열들을 창안하고 이들의 모형시험 결과를 비교 분석한 내용이 기술되었다. 구상선수의 형상을 결정짓는 7가지의 변수를 생각하고 이들을 체계적으로 변화시켜 구상선수 형상변화의 영향을 실험적으로 조사하도록 계획하였다. 총 23개 선형의 모형선을 제작하였으며, 각 선형에 대하여 저항시험, 유선조사시험 및 선측파고 계측시험이 수행되었다. 구상선수의 형상변화와 모형시험 결과와를 상호 비교 분석하기 위하여 유사한 특성의 구상선수들을 모아서 9개 그룹으로 분류하였으며 각 그룹 별 저항성분의 변화 경향을 분석해 본 결과 비대선에서는 형상저항이 전저항에 지배적인 영향이 있음을 확인하였다. 또한 모형시험 결과 및 이의 통계적 분석 자료로부터 비대선에서는 구상선수 주위의 유선의 방향이 저항성분들과 밀접한 관계가 있으며 저항성분들 중에서도 형상저항과 더욱 밀접한 관계가 있다는 사실을 발견하였다.

• 대한조선학회 특별논문집
• /
• 대한조선학회 2005년도 특별논문집
• /
• pp.31-37
• /
• 2005

An attempt to improve the speed performance through the minimizing in wave resistance has been done by an application of gooseneck and no bulb type to bulbous bow for the DSME 78,500 Class LPG Carrier on the basis of the CFD calculation and comparatives model tests. The hydrodynamic characteristics according to the variation of the shape of Cp-curve, design load water line, frame line and bulbous bow that have an important effect on the wave resistance has been evaluated/calculated by ship-flow code. A wide variety in hull variation have been tried to have a good hull form with three types of fore-body hull forms mainly classified by the shape of bulbous bow. The speed performances for the three final hull forms with different bulbous bows have been evaluated through the model tests.

• 대한조선학회지
• /
• 제10권2호
• /
• pp.19-28
• /
• 1973

This paper deals with a problem for determining the bulbous bow ship from which pertains to the study of the theoretical ship form planing method. In this paper has been determined the bulbous bow ship form which is a similar in geometric particulars with the conventional liner ship G.T.10, 000 by adopting the variable method for finding the optimum ship form by A.Y.C. Lee and the streamline tracing method by T. Inui and P.C. Pien. Each resistance performance is examined by the towing test and is compared with one another. The followings are the outcome of this study: Among the 5 type models, the bulbous bow ship form M.S. B 1120 is the most excellent for the resistance performance. The effect for the wave resistance is very sharp according to the difference of the bottom flattening of theoretical ship form. The optimum value of the bulbous bow for wave resistance can be obtained by the variable method mentioned above, and for the series of(Main hull+Bulb)opt., ${\alpha}=75/25$, the value is $f{\approx}0.11$.

• 대한조선학회논문집
• /
• 제55권3호
• /
• pp.265-273
• /
• 2018

Direct numerical and large eddy simulations of transitional flows around studs installed on flat plate and bulbous bow have been performed to investigate an effectiveness of turbulence stimulators on laminar-to-turbulence transition at a very low speed. The flow velocity was determined to be 0.366m/s corresponding to 4 knots of full-scale ship speed when the objective ship was Kriso container ship. The spatial evolution of skin friction coefficient disclosed that a fully development of turbulence was observed behind the second stud installed on flat plate while a rapid transition from laminar to turbulence gave rise to the fully development of turbulence behind the first stud installed on bulbous bow. A comparison of streamwise mean velocity profiles showed that the viscous sublayer and log-layer were in good agreement with previous results although the friction velocity of Smagrosinsky sub-grid scale model was about 10% larger than that of direct numerical simulation. While the turbulence intensities of bulbous bow was similar to those of flat plate in inner region, larger intensities of turbulence were observed in outer region of bulbous bow than those of flat plate.

• 대한조선학회지
• /
• 제4권1호
• /
• pp.1-34
• /
• 1967

The wave-cancelling effects of a large bulbous bow on the coastal passenger boat have been investigated in deep and shallow water. The following characteristics have been cleared through resistance tests with the model of the Korea standard type coastal passenger vessel(LWL=25.8m, B=5.5m, T=1.65m) equipped with large bulbous bows of various sizes. (1) Over the range of Froude Number 0.30, the wavemaking resistance coefficients decrease 30% or more. (2) The optimum location of bulb center is around 8% L from F.P. (3) On the 120 G.T. passenger coaster which has a speed corresponding to Froude Number 0.34, the most advantageous bulb is the one whose $a_0/L$ is about 0.28. When the speed is up, the bulb radius should be increased accordingly. (4) The large bulbous bows are effective in shallow water to a water depth of H/T=2.0. (5) Tendency to the increase in the resistance of the hull with large bulbous bow in the shallow water is generally smaller than that of the hull without bulb.

• 한국해양공학회지
• /
• 제34권4호
• /
• pp.272-276
• /
• 2020

This paper presents an optimization process for a catamaran hull form. The entire optimization process was managed using the CAD-CFD integration platform CAESES. The resistance of the demi-hull was simulated in calm water using the CFD solver STAR-CCM+, and an inviscid fluid model was used to reduce the computing time. The Free-Form Deformation (FFD) method was used to make local changes in the bulbous bow. For the optimization of the bulbous bow, the Non-dominated Sorting Genetic Algorithm (NSGA)-II was applied, and the optimization variables were the length, breadth, and angle between the bulbous bow and the base line. The Lackenby method was used for global variation of the bow of the hull. Nine hull forms were generated by moving the center of buoyancy while keeping the displacement constant. The optimum bow part was selected by comparing the resistance of the forms. After obtaining the optimum demi-hull, the distance between two demi-hulls was optimized. The results show that the proposed optimization sequence can be used to reduce the resistance of a catamaran in calm water.

• 수산해양기술연구
• /
• 제47권4호
• /
• pp.435-442
• /
• 2011

In an attempt to respond to the increase in international oil prices and reduce operating expenses, ship remodeling was carried out on a 740ton class tuna purse seiner. To strengthen the competitiveness of the fisheries industry by improving vessel performance, a bulbous bow was newly equipped. The slipway and rudder area were also lengthened and enlarged with the propeller and main engine remained unchanged. To reduce the hull resistance, a circle type bulbous bow was attached on the hull behind bow thruster and thus the cost for exchanging electrical equipment for bow thruster was reduced. The new rudder area was expanded 15% more than the old one within the extent that the existing mechanical control part and rudder stock were not changed. To prevent fishing net damage and stabilize wake field, slipway was lengthened to the optimal position. All of the new design of remodeling parts went through the model tests in towing tank and CWC. Besides resistance test, all of necessary model test results were delivered for hydrodynamic character for the modified ship. The maneuvering simulation to verify that the remodeled ship satisfies the IMO rules was performed in both zigzag and turning tests. The estimated resistance with new bulbous bow and lengthened stern was reduced by 4.8% in the 2-dimensional analysis and 17.4% in the 3-dimensional analysis in comparison of conventional ship. The average reduction of resistance was estimated about 10%. Maneuvering character of modified hull form was found to satisfy all regulations under IMO. The remodeling of tuna purse seiner can not only improve fishing performance but also contribute to reduction of operating cost by saving energy for the fisheries industry.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제5권2호
• /
• pp.302-312
• /
• 2013

While displacement type Deep-V mono hulls have superior seakeeping behaviour at speed, catamarans typically have modest behaviour in rough seas. It is therefore a logical progression to combine the superior seakeeping performance of a displacement type Deep-V mono-hull with the high-speed benefits of a catamaran to take the advantages of both hull forms. The displacement Deep-V catamaran concept was developed in Newcastle University and Newcastle University's own multi-purpose research vessel, which was launched in 2011, pushed the design envelope still further with the successful adoption of a novel anti-slamming bulbous bow and tunnel stern for improved efficiency. This paper presents the hullform development of this unique vessel to understand the contribution of the novel bow and stern features on the performance of the Deep-V catamaran. The study is also a further validation of the hull resistance by using advanced numerical analysis methods in conjunction with the model test. An assessment of the numerical predictions of the hull resistance is also made against physical model test results and shows a good agreement between them.