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Accuracy of Potential Flow Methods to Solve Real-time Ship-Tug Interaction Effects within Ship Handling Simulators

Jayarathne B. N., Ranmuthugala D., Fei J.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2014

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Vol. 8 no. 4

497--504

EN

The hydrodynamic interaction effects between two vessels that are significantly different in size operating in close proximity can adversely affect the safety and handling of these vessels. Many ship handling simulator designers implement Potential Flow (PF) solvers to calculate real-time interaction effects. However, these PF solvers struggle to accurately predict the complicated flow regimes that can occur, for example as the flow passes a wet transom hull or one with a drift angle. When it comes to predicting the interaction effects on a tug during a ship assist, it is essential to consider the rapid changes of the tug’s drift angle, as the hull acts against the inflow creating a complicated flow regime. This paper investigates the ability of the commercial PF solver, Futureship®, to predict the accurate interaction effects acting on tugs operating at a drift angle during ship handling operations through a case study. This includes a comparison against Computation Fluid Dynamics (CFD) simulations and captive model tests to examine the suitability of the PF method for such duties. Although the PF solver can be tuned to solve streamline bodies, it needs further improvement to deal with hulls at drift angles.

2

Research on hydrodynamic properties of annular cavitator with water injection

Zhenyu Jiang Zhenyu, Min Xiang Min, Mingdong Lin Mingdong, Weihua Zhang Weihua, Shuai Zhang Shuai

Polish Maritime Research

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2012

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nr 4

11-14

EN

Annular cavitator with water injection is one of the key parts of the long-range supercavitating vehicle powered by water ramjet. In this paper, hydrodynamic properties of annular cavitator are studied numerically. The standard k ~ ĺ turbulence model is coupled with the Reynolds Averaged Navier-Stokes (RANS) equations to model the natural supercavitation process. The multiphase flow is considered as a mixture of varying density and modeled by the mass exchange equations. To fully understand this process, numerical simulations were performed for different annular cavitators. Computational Fluid Dynamics (CFD) results, including the pressure distribution and forces acting on the cavitator surface, mass flow and pressure loss of water injection, various supercavity sizes, were obtained and analyzed. The pressure distribution on the cavitator surface was significantly changed which resulted in 4 ~ 6% increase of the total drag of the vehicle. The results show that the mass flow and velocity of the injection water is mainly dependent on the tube size, while the total pressure loss of the water injection is mostly related to the outlet pressure. Supercavity generated by annular cavitator is smaller than that of the discal one. Based on the correlation analysis of the supercavity size and other factors, it could be concluded that the contraction of the cavity size is mainly caused by the diffluent mass flow of the water injection.

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Increasing ship propulsion efficiency as an alternative to help reduce fuel consumption and CO2 emmision. Part 1

Szelangiewicz T., Żelazny K.

Journal of Polish CIMAC

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2012

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Vol. 7, no 1

227-233

EN

From 2013 onwards EEDI for newly built ships will become mandatory. Ships meeting the CO2 emission standards will be granted energy certificate for needed for exploitation. The article presents the EEDI in the current form, energy certification procedure as well as reduction of CO2 emission planned for coming years (Part I). The majority of ships built at present, meets the CO2 emission standards for 2013, yet their further decrease in subsequent years will consequently necessitate further actions as well. One of them is ship hull design of smaller resistance values and higher propulsion efficiency. The article (Part II) presents calculation results of the numerical analyses (CFD) performed for an actually built ship, aiming at decreasing propulsion power and therefore the EEDI value as well.

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Increasing ship propulsion efficiency as an alternative to help reduce fuel consumption and CO2 emmision. Part 2

Szelangiewicz T., Żelazny K.

Journal of Polish CIMAC

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2012

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Vol. 7, no 1

235-244

EN

From 2013 onwards EEDI for newly built ships will become mandatory. Ships meeting the CO2 emission standards will be granted energy certificate for needed for exploitation. The article presents the EEDI in the current form, energy certification procedure as well as reduction of CO2 emission planned for coming years (Part I). The majority of ships built at present, meets the CO2 emission standards for 2013, yet their further decrease in subsequent years will consequently necessitate further actions as well. One of them is ship hull design of smaller resistance values and higher propulsion efficiency. The article (Part II) presents calculation results of the numerical analyses (CFD) performed for an actually built ship, aiming at decreasing propulsion power and therefore the EEDI value as well.

5

Convection of internal variable methodology in Computational Fluid Dynamics solutions for thixoforming modelling

Macioł P.

Computer Methods in Materials Science

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2007

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Vol. 7, No. 1

112-118

EN

During thixoforming, the deformed material is in semi-solid state. From numerical point of view, such materials are difficult to simulate because of gathering some features of solid materials and some of fluids. Materials properties are history dependent like in solids, while deformations could be extremely high, like in fluids. The typical solutions of structural analysis, based on Lagrangian motion description are difficult because of remeshing, which is needed in short time intervals. Frequent remeshing operations increase time consumptions and decrease the accuracy of solution. On the other hand, typical Computational Fluid Dynamics (CFD) solutions, usually based on Eulerian motion description, are ineffective when domain borders are changing. Because of material points are detached from mesh nodes, the history dependent parameters of the material are also very difficult to introduce. On the contrary, in the third possible formulation, Arbitrary Lagrangian Eulerian (ALE), the material points are not bound with mesh nodes and domain geometry could change. In ALE formulation each time step is divided into Lagrangian and Eulerian steps, what assures that history of material could be included and the calculation domain is reproduced properly by the mesh. Therefore, ALE formulation seems to be the best solution in the most thixoforming cases. The disadvantages of this method are the time consumptions and some inaccuracy of approximation needed between both steps. In the cases when the domain of solution is unchangeable, Eulerian formulation could be more promising than ALE. The Eulerian solution is easier to implement, as well as computational round-offs are less significant. The difficulties connected with history dependent parameters could be solved with “internal variable convection”. After classical time step, when new velocities in nodes are computed, the convection step is carried out. While velocity field is known, the convection of internal variable values could be calculated. The changes of internal variable due to material processes could be included as a source stream. The internal variable convection methodology allows to adapt typical CFD codes for thixoforming simulations, with complying viscosity changes in time. This approach also makes very high deformations relatively easy to compute. In this paper, the assumption and proposition of implementation of internal variable convection into thixoforming modelling is presented.

PL

Tiksoforming jest stosunkowo nową metodą formowania. Polega ona na nadawaniu znacznego stopnia odkształcenia materiałowi w stanie stało-ciekłym. Z numerycznego punktu widzenia, procesy te są trudne do modelowania, co jest efektem występowania zjawisk charakterystycznych zarówno dla cieczy, jak i ciał stałych. Własności materiału są zależne od czasu, podobnie jak w materiałach stałych, podczas gdy odkształcenie może być bardzo duże, podobnie jak w cieczach. W artykule zaprezentowano przegląd obecnie istniejących rozwiązań numerycznych, opartych głównie na metodach dynamiki płynów, z zastosowaniem opisu kinetyki wg metody Eulera lub Arbitrary Lagrangian Eulerian (ALE). Wykazana została potrzeba opracowania nowej metody symulacyjnej dla zależnych od czasu materiałów poddawanych formowaniu tiksotropowemu. Opisana została metoda konwekcji zmiennej wewnętrznej dla eulerowskiego opisu kinetyki. Przedstawiona została implementacja metody jako procedur użytkownika komercyjnego pakietu ADINA-F. Zaprezentowano przykładowe wyniki dla prostych przepływów tiksotropowych.