International Shipbuilding Progress - Volume 64, issue 1-2

Authors: Hu, Jun-ming | Li, Tie-li | Lin, Yan | Guan, Guan | Ji, Zhuo-shang

Article Type: Research Article

Abstract: According to the forming reason and classification of the hull resistance, this paper puts forward a three dimensional RANS method to solve the wave-making resistance. The obtained numerical results are compared with the results obtained from numerical program based on Rankine source boundary element method and the results obtained from Experimental fluid dynamics (EFD) method. The conclusion is drawn that the three dimensional RANS method matches well with EFD method, and its accuracy is higher than Rankine source method. From the results of the used methods it appears that the value of shape factor ( 1 + k ) …for three dimensional RANS method is slightly increased with the increase of Froude number, the free surface wave system of three dimensional RANS conforms to the characteristics of the Kelvin wave system, the height of wave crest for three dimensional RANS method is bigger than Rankine source method, while the wave trough is lower, and the variation tendency of wave profile based on three dimensional RANS method is almost the same with Rankine Source method. The proposed method is proved to be appropriate for engineering application. Show more

Keywords: Three dimensional RANS method, Rankine source method, EFD method, wave resistance, shape factor, wave pattern

DOI: 10.3233/ISP-170128

Citation: International Shipbuilding Progress, vol. 64, no. 1-2, pp. 1-23, 2017

Authors: Boote, D. | Pais, T. | Vergassola, G. | Tonelli, A. | Gragnani, L.

Article Type: Research Article

Abstract: After a long period in which the most attractive characteristic of a motor yacht was represented by her maximum speed, nowadays the target has moved towards comfort on board which became the fundamental parameter to deal with in the yacht design process. Noise and vibration, together with seakeeping behaviour, became the fundamental subjects on which the research effort of shipyards and technical offices turned on. Since many years the Department of Electrical, Electronic, Telecommunication Engineering and Naval Architecture (DITEN) is involved in a research on the dynamic behaviour prediction of large motor yachts in cooperation with one of the …most important Italian shipyards. In this perspective the assessment of the dynamic properties of materials used for the vessel construction, such as the damping coefficient, is an important step to perform preliminary analyses for vibration and noise levels. This paper is focused on the definition of the damping coefficient of laminated glass, which is a complex material commonly used for windows in the current yacht market. As a matter of fact the actual trend of using larger and larger windows for owner’s cabins and saloons could represent a critical point in terms of noise and vibrations and makes the laminated glass dynamic characterization a fundamental issue to be investigated. Different experimental modal methods to obtain the damping coefficient at natural frequencies are applied to laminated glass specimens, while the Reverberation Time test is proposed to assess the coefficient in the whole frequency range of interest. In the final part of the paper, a comparison between the results of different methods is presented. Show more

Keywords: Damping coefficient, laminated glass, dynamic structural analysis, yacht structures

DOI: 10.3233/ISP-170131

Citation: International Shipbuilding Progress, vol. 64, no. 1-2, pp. 25-40, 2017

Authors: Volenyuk, L.S. | Rashkovskyi, A.S.

Article Type: Research Article

Abstract: The changing forces acting on a ship during launching from a longitudinally sloping slipway can be divided into four stages: the 1st stage – from beginning of ship movement until the launching runners or the ship’s aft end contacts the water; 2nd stage – from the end of 1st stage until the ship begins to float off the ways; 3rd stage – from the end of 2nd stage until the ship paces the slipway threshold and is fully afloat; 4th stage – from the end of 3rd stage until comes to a full stop. The biggest danger for a ship during the launch is …the end of stage 2 and the beginning of stage 3, when tipping is possible as the ship rotates around the slipway threshold; also as the ship pivots on the slipway’s threshold there are large concentrated forces imparted on the forward section of the ship due to pivoting pressures (the difference between the mass of the ship and launching devices and the rising buoyancy). This paper presents, for the first time, a new analysis method of taking into account the possibility of a tanker tipping during launching on pneumatic airbags. Launching calculations and diagrams for both the traditional and pneumatic airbags launching are presented along with a comparative analysis of the two launching methods. The analysis showed that during launching using pneumatic airbags, float off begins earlier than during a traditional launch. This earlier float off does not increase the risk of tipping but does increase the pivoting pressure due to the increased buoyancy from the airbags. Show more

DOI: 10.3233/ISP-170136

Citation: International Shipbuilding Progress, vol. 64, no. 1-2, pp. 41-50, 2017

Authors: Hu, Jun-ming | Li, Tie-li | Lin, Yan | Guan, Guan | Zheng, Zi-bo

Article Type: Research Article

Abstract: This paper adopts virtual tank experimental technology to study ship rapidity performance. Based on RANS method, a new method is put forward to predict the speed and power performance of full scale ship. The open water performance of propeller model, the resistance performance of ship model and the self-propulsion performance of ship model are numerically calculated. Through the analysis of rapidity numerical results of fishing ship and the change law of wake flow field, some conclusions can be drawn. The numerical prediction accuracy of propeller open water efficiency has a direct influence on total thrust efficiency. The interference between hull, …propeller and rudder leads to the formation of a lower pressure zone on stern hull surface and rudder surface. The axial velocity and radial velocity are affected by the interference between the flow of hull stern and propeller, the absolute value of axial velocity on blade leaf is smaller than that on blade back, and the radial velocity induces vortices on the blade tip of the propeller. The increase of propeller rotation speed nearly has no effect on the free surface wave pattern. The prediction results deviations of full scale ship speed and propeller rotation speed between RANS method and EFD method are 0.04 kn and 0.4 r/min, and therefore they are negligible. The proposed method can provide reference for engineering application. Show more

Keywords: RANS method, EFD method, power performance, self-propulsion factor, speed prediction

DOI: 10.3233/ISP-170137

Citation: International Shipbuilding Progress, vol. 64, no. 1-2, pp. 51-78, 2017

Authors: Liu, Ge | Lin, Yan | Guan, Guan | Yu, Yan-yun

Article Type: Research Article

Abstract: The sloshing induced by partial loading is violent when a resonance condition occurs. Given strong nonlinearity, rapid and accurate prediction of sloshing loads under resonance conditions is the key factor in the design of LNG (liquefied natural gas) cargo tanks. Therefore, a numerical technique based on CFD (computational fluid dynamics) technique was developed for sloshing simulations. Next, a series of physical tests were designed to validate its accuracy. Sloshing characteristics under resonance conditions is discussed experimentally by profiling the free surface and sloshing loads. The resonant test conditions were selected for simulations. Both the shape of the free surface and …the sloshing pressure were compared with the test results. The computational model and parameters were also verified. It can be proven that based on reductions in the large computational expense, the numerical simulation has good accuracy for sloshing simulations. Show more

Keywords: Sloshing, resonance, independent type C LNG tank, numerical simulation, experimental investigation

DOI: 10.3233/ISP-170138

Citation: International Shipbuilding Progress, vol. 64, no. 1-2, pp. 79-100, 2017

Authors: Palaniappan, M. | Subramanian, V. Anantha

Article Type: Research Article

Abstract: Oceanographic research vessels are fitted with acoustic sonar transducers at the bottom keel region. For a ship underway, atmospheric air gets mixed naturally with the surface water in the presence of wind and waves. Bubbles get entrapped in the region within the draft of the vessel and flow in the stream past the vessel. Literature records show that the bubbles are formed in the upper regions (made worse by the pitching motion) below the surface. When they flow immediately below and in the region of the sonar transducer resulting in bubble sweep-down phenomenon, they directly interfere with the acoustic transmission …and deteriorate the functioning of the sonar transducer. Degradation of performance of the acoustic transducer seriously limits the mission capability of the vessel. This is a major concern and there is no complete remedy as of date, for the avoidance of the bubble formation in the flow stream. This paper describes a hydrodynamic re-design approach for the hull geometry in the forward region and the creation of an effective bubble diverter bow. A new modified bow form is investigated to help in deflecting the stream lines away from the location of the sonar transducer. The strategy in the approach here is to design the bow region to control hydrodynamic flow such that the bubbles-entrapped water of the upper surface layers is strategically diverted to flow side-ways of the hull or at the bottom side-ways well away from the location of the sonar transducer. Numerical flow simulations for the developed hull form using CFD tools demonstrate that the streamlines can be effectively thus diverted without degradation of the performance of the sonar transducer. The strategy for the hull form design is evolved by parametric variation of the side-shape using computer aided surface generation tools. The parameters influencing drag as well as diversion of the streamlines are the length parameter of the bubble diverter bow at side, the cross-sectional area parameter at a pre-defined section at the forward and the wetted surface parameter of the bubble diverter bow. The beneficial effect of the bubble diverter bow is to be weighed against increased hull resistance. The validation studies include simulation of the flow and drag assessment and comparison from towing tank tests as well. Three hull forms are created and the streamlines traces are studied in these cases respectively. The results demonstrate that a minor re-design of the forward sides of the hull form can drastically minimize the bubble streamline interference at the sonar transducer without penalty on the resistance. A major breakthrough is offered in the mitigation of bubble sweep down by the new design. Show more

Keywords: Bubble sweep-down, oceanographic research vessel, bubble diverter bow, acoustic transducer, streamline trace

DOI: 10.3233/ISP-170139

Citation: International Shipbuilding Progress, vol. 64, no. 1-2, pp. 101-126, 2017