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가설 설정
- 10. Definition of vertical angle and distance between skegs in stern skeg arrangement.
제안 방법
- Hull form optimization for twin skeg was investigated on the position of LCB, vertical angle of skeg and distance between skegs. After study of optimum LCB position, the stem of twin skeg hull was modified and developed by using the stem hull form for single of skeg.
- The flow computational conditions of flow field are summarized in Table 5. All numerical calculations of hull form optimization for both skeg ships were conducted by application of viscous free surface flow for the hull with rudder and propeller influence solving the unsteady hull-propeller interaction using propeller body force distribution based on lifting surface theory.
- First, vertical angle variation of skeg was conducted to improve the propulsive performance.
- In order to determine the range of draught and speed to be optimized for ULCS, the operating profiles which have already analyzed by ship owners for other size container ships were investigated by frequency analysis of operating draught and speed. The most frequent draught and speed of two existing ships optimized for each operating profile is shown in Table 16.
- Model tests were carried out in the towing tank at Hyundai Maritime Research Institute (HMRI) to validate the computational results for the hull form optimization and to evaluate the resistance and propulsive performance of optimized hull form. The dimension of the towing tank, maximum speed and type of wave maker are shown in Table 13.
- The first, initial design procedures are described for ULCS with economic assessment under environmental regulations and various requirements of potential ship owners with design items and factors to be considered.
- All hull form optimization with variation methods of hull was conducted extensively through flow simulation, investigation and performance assessment from CFD calculation. The model tests for both optimized hull forms were carried out to get the data and confirm the results of hull form optimization.
- The second, the characteristics and performance of single and twin skeg ships are compared based on information from initial design and optimized hull form for both ships in this paper.
- For single skeg ship, optimization for forward hull form including bulbous bow variation was conducted mainly. The stem hull form of twin skeg hull was modified and developed by using the stem of single skeg after study of optimum Longitudinal Center of Buoyancy (LCB) position. And then, optimization of twin skeg hull form was investigated around stern skegs.
- The third, hull form optimization to improve resistance and propulsive performance at design draught and speed was conducted for single and twin skeg ships with the same dimensions by several variation and optimized hull form for each skeg type was derived through comparison and analysis with the results of CFD and model tests.
- Through the investigation on ships which have large dimension and relatively wide breadth, both single and twin skeg container ships were designed and compared for their own characteristics.
대상 데이터
- 16,000TEU single skeg ship designed at relatively high speed, 25.5 knots (Fn=0.214), was selected for initial hull form from data base system and modified to initial hull form (Ship SI) of single skeg ship.
이론/모형
- All data and results of the CFD calculation were extrapolated to the full scale using ITTC 1978 Performance Prediction Method (ITTC, 1978).
- In this work, a commercial grid generation code was used to make surface and spatial grid system. The distance of the first grid point of the ship surface was maintained 50 < y+ < 150 that is within a low-law region.
- In this work, the four step procedures of the initial design and hull form optimization to maximize economic and propulsive performance are presented for ULCS.
- The dimension of the towing tank, maximum speed and type of wave maker are shown in Table 13. The extrapolation method to the full scale is using ITTC 1978 Performance Prediction Method. The model with scale ratio of about 1/45.
- The numerical calculation was conducted to optimize the hull form by using a commercial CFD code (WAVIS ver.2) (Kim et al., 2011) which has been developed by Korean Research Institute for Ships and Ocean Engineering (KRISO) and is able to generate the grid of the single skeg hull automatically and calculate potential and viscous free surface flow with the change of trim and sinkage of ships and self-propulsion performance of ships by solving interaction between viscous free surface flow of hull and propeller influence from calculation based on lifting surface theory. The main characteristics of CFD code are RANS (Reynolds Averaged Navier-Stokes) method for governing equation, Finite Volume Method (FVM) for integration and LS (Level-Set method) for the effect of free surface.
성능/효과
- As for main engine tuning at part load, the proportions of ETOTAL for single and twin skeg hulls compared to Ship SA and Ship TA are 94.5 % and 92.2 %. In case of main engine tuning at low load, the proportions of ETOTAL for single and twin skeg hulls are saved more as Table 20.
- Table 10 shows the simulation results of the resistance and propulsive performances with variation of the vertical skeg angle, which indicates that as vertical angle increases, resistance performance is getting better, but on the contrary propulsive performance is getting worse. From the simulation results, -15˚ was chosen as the optimized skeg angle with the improvement of DHP by 2.2 % compared with the optimized hull form for LCB.
- for optimized hull forms (Ship SAO and TAO) based on operating profile compared to hull forms (Ship SA and Ship TA) optimized at design draught and speed. The total saving proportion of ETOTAL for single skeg hull is 4.1 % and in case of the twin skeg hull, the saving effect ETOTAL of is 6.5 % which is relatively bigger than single skeg hull because ETOTAL of the twin skeg hull optimized at design draught and speed is worse than single skeg hull.
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