International Shipbuilding Progress - Volume Pre-press, issue Pre-press

Authors: Shin, Keun Woo | Andersen, Poul

Article Type: Research Article

Abstract: It is important to make predictions of cavitation-induced erosion risk on ship propellers in the design phase. Since a cavitation tunnel test on a propeller model coated by soft paint, that is, a standard experimental method for evaluating erosion risk, is costly and time-consuming, numerical methods are necessary for erosion risk predictions. DES is made for cavitating flows around the propeller with a numerically modelled hull wake at the inflow. After achieving a converged solution, an erosion risk index is computed in each cell connecting to the blade surface and accumulated over a propeller rotation. Cavitation simulations are made …for two propellers designed for a single-screw ship, of which one showed an erosion indication and the other showed no indication after cavitation tunnel tests with soft paint coating. Three index formulations are compared with the experiment result. The high value region of Index 1 based on the potential energy density of collapsing bubbles corresponds better with the eroded spot indicated by partial and complete paint removals in the experiment than those of the other indices. The maximum value of Index 1 for the non-eroded propeller is lower by more than an order of magnitude than that for the eroded one, whereas the maximum values of the other indices are of the same order of magnitude for both propellers. The validation of Index 1 is in agreement with the criterion that the maximum index needs to be below 1,000 J/m3 for erosion-free propeller designs. The design evolution based on the erosion risk index and propulsive efficiency from CFD shows that it can be a practical tool for a quantitative evaluation of blade surface erosion risk in the propeller design phase. Show more

Keywords: Ship propeller, cavitation, erosion, CFD, DES

DOI: 10.3233/ISP-201002

Citation: International Shipbuilding Progress, vol. Pre-press, no. Pre-press, pp. 1-22, 2020

Authors: Wellens, Peter

Article Type: Editorial

DOI: 10.3233/ISP-210526

Citation: International Shipbuilding Progress, vol. Pre-press, no. Pre-press, pp. 1-2, 2020

Authors: Lena, Christian | Bonci, Matteo | van Walree, Frans

Article Type: Research Article

Abstract: Ships can experience serious difficulties in keeping a straight course when sailing in stern-quartering seas. Design modifications like the addition of stern passive fins, or the modification of active control surfaces, are common solutions to improve the ship course-keeping. However, the success of such design modifications depends on the delicate balance between the excitation forces induced by the waves on the appended hull, the stabilization forces provided by the lifting surfaces as appended fins, and the steering forces provided by the control surfaces. This research investigates which of these aspects of a ship design play a concrete role in improving …the ship course-keeping in waves. The study is carried out with the intention of looking at the different behaviors of the ship originating from different stern appendages configurations. Three modifications of stern appendages on three different ship hulls were investigated in various mild-to-rough sea conditions. The behavior of the vessels were simulated using a time domain, boundary element potential method, with the addition of semi-empirical formulations for the modelling of the stern lifting surfaces. The simulations were carried out in long crested irregular waves at three different direction, using the JONSWAP spectrum. The results showed that although larger stern appendages improve the directional stability of relatively large and slow vessels, in most cases they worsen their course-keeping ability, increasing the yaw motions. For smaller and faster vessels instead, passive and active fins tend to improve the course-keeping, because at high speed the lift provided by the appendages stabilizes the vessel. This effect is compensated by the wave excitation force at lower speed. Similarly to yaw, the roll motions increases with larger stern appendages. Show more

Keywords: Course-keeping, directional stability, manoeuvrability-in-waves, following seas, panel method, stern appendages

DOI: 10.3233/ISP-201006

Citation: International Shipbuilding Progress, vol. Pre-press, no. Pre-press, pp. 1-29, 2020

Authors: van der Eijk, Martin | Wellens, Peter

Article Type: Research Article

Abstract: This paper presents the comparison of a self-conducted towing tank experiment with the simulation results of a calibrated state-of-the-art strip-theory method and a first-principles numerical method. The experiment concerns a Rigid Inflatable Boat (RIB) in moderate-to-high irregular waves. These waves result in bow emersion events of the RIB. Bow re-entry induces vertical accelerations which, in reality, can lead to severe injuries and structural damage. State-of-the-art methods for predicting the vertical acceleration levels are based on assumptions, require calibration and are often limited in application range. We demonstrate how the vertical acceleration as a function of time is found from a …3D numerical method based on the Navier–Stokes equations, employing the Volume of Fluid (VoF) method for the free surface, without any further assumptions or limitations. 2D+t strip theory methods like Fastship are based on the mechanics of wedges falling in water. The 3D numerical method that is part of the software ComFLOW is compared to previous research on falling wedges in 2D to investigate the effect of air and to find suitable grid distances for the 3D simulation of the RIB. The 3D RIB simulations are compared to Fastship and the experiment. With respect to the experiment, the ComFLOW simulations show a slight underestimation of the levels of heave and pitch. The underestimation of Fastship is larger. The prediction of acceleration in ComFLOW is hardly different from the experiment and a significant improvement with respect to Fastship. ComFLOW is demonstrated to predict acceleration levels better than before, which creates opportunities for using it in seakeeping optimization and for the improvement of methods like Fastship. The properties of the RIB and the experiment are available as open data at Wellens (2020 ). Show more

Keywords: Ship model test, irregular waves, high speed craft, bow re-entry, CFD, multiphase flow

DOI: 10.3233/ISP-201005

Citation: International Shipbuilding Progress, vol. Pre-press, no. Pre-press, pp. 1-26, 2020

Authors: Mauro, Francesco | Benci, Aron | Ferrari, Victor | Della Valentina, Enrico

Article Type: Research Article

Abstract: In some specific environmentally protected areas, conventional mooring systems cannot be used by large yachts for stationing at anchor and therefore, the adoption of a dynamic positioning system is required. It becomes then necessary to evaluate the station keeping capabilities of a yacht since the early-design stage. Adopting a quasi-static approach, it is possible to perform a standard capability analysis, as commonly done for the offshore industry, obtaining a capability plot as output. However, capability plots are referring to specific wind-wave correlation that are not covering all the possible wave combinations present in a sea area. Here, it is proposed …to use a scatter diagram approach for the dynamic positioning analysis of a large yacht, considering the specific sea areas where the yacht shall operate, in order to figure out the downtime period of the DP system per each sea area. The proposed method can be coupled with traditional ship motions analysis, leading to a combination between comfort assessment and DP predictions. In the present work, use has been made of a traditional displacement yacht 72 m long, comparing five different DP system configurations and evaluating an enhanced comfort ranking combining ISO AWI-22834 guidelines for large yachts with ISO AWI-22822 DP analysis. Show more

Keywords: Large yachts, comfort on-board, DP predictions, early-design stage, ship motions

DOI: 10.3233/ISP-210508

Citation: International Shipbuilding Progress, vol. Pre-press, no. Pre-press, pp. 1-28, 2020

Authors: Rashkovskyi, A.S. | Shchedrolosiev, A.V. | Neiman, V.M. | Kanash, O.Y.

Article Type: Research Article

Abstract: Investigations of pneumatic transport of bulk materials used in shipbuilding have carried out. Their abrasiveness, wear of straight and curved sections of pipelines were investigated. Theoretically, the dependences of the amount of wear on various factors were defined: abrasiveness and concentration of transported particles, flow rate, pipe diameter and wear resistance of its material, structural and operational features of the transport system, etc. Formulas for determining the maximum useful life of straight and curved sections of pipelines are obtained. Theoretical results confirmed experimentally.

Keywords: Pneumatic transport, bulk materials, composite floating docks, flow rate, wear resistance

DOI: 10.3233/ISP-209004

Citation: International Shipbuilding Progress, vol. Pre-press, no. Pre-press, pp. 1-14, 2020

Authors: Garcia Agis, Jose Jorge | Brett, Per Olaf | Erikstad, Stein Ove

Article Type: Research Article

Abstract: BACKGROUND: Understanding how and why the development of conceptual ship designs sometimes become ineffective is essential for ship design firms. Our proposition is that in many projects, uncertainty influences negatively the effectiveness of the decision-making process. OBJECTIVE: The objective of this article is to quantify the perception of uncertainty in conceptual ship design processes. METHODS: In this article, we propose a research model to study such a phenomenon. The research model is tested using multivariate regression analysis, building on a survey conducted among 23 shipping companies. RESULTS: Our model suggests that 14% (R …2 ) of the variability in the effectiveness of decision-making processes in ship design can be explained by changes in the perception of uncertainty. We can extract three interesting insights from this research work for the ship design practitioners as to how to improve the effectiveness of their design processes: (i) put more effort into the contextual factors affecting the ship design process, (ii) improve the communication with vessel owners and other stakeholders, and (iii) improve the agility of the design process. CONCLUSIONS: This study contributes to research on uncertainty in ship design processes by: (a) proposing an investigative model, (b) developing and testing a survey instrument and (c) running a multivariate regression analysis to study the effect of perceived uncertainty on the effectiveness of decision-making processes in conceptual ship design. Show more

Keywords: Uncertainty, Ship design, decision-making effectiveness, multivariate regression analysis, survey

DOI: 10.3233/ISP-209003

Citation: International Shipbuilding Progress, vol. Pre-press, no. Pre-press, pp. 1-32, 2020