View non-flash version
January 2013 www.sname.org/sname/mt ( abstracts )SNAME Paper Abstracts A Simple Veri?cation Test for Nonlinear Flow Calculations Around a Ship Hull Steadily Advancing in Calm Water BY FRANCIS NOBLESSE, LIJUE WANG, AND CHI YANG PUBLISHED IN THE SEPTEMBER JOURNAL OF SHIP RESEARCHSimple analytical relations are given that can readily be applied to verify a critical aspect of numerical predictions of fully nonlinear free-surface ows around ship hulls steadily advancing in calm water. e relations do not involve the ow eld equations; that is, they are only based on the boundary conditions at the ship hull surface and at the free surface. ese boundary conditions have a predomi- nant inuence on free-surface ows around advancing ship hulls. e analytical relations are exact for inviscid ows, and can be applied to numerical methods that solve either the Laplace equation (potential-ow methods) or the Euler ow equations (CFD Euler-ow methods). ey provide a simple test to ver- ify if numerical predictions given by nonlinear potential-flow or Euler-flow methods cor- rectly satisfy the hull-surface and free-surface boundary conditions along the contact curve between the hull surface and the free sur- face. e relations might also be used to verify CFD methods that solve the RANS equations if they are applied at the edge of the viscous boundary layer. e analytical test can iden- tify an inconsistency, which might point to a method issue related to a feature of a numer- ical method (e.g., a numerical-dierentiation scheme) or an implementation issue in the implementation of the method (e.g., a poor discretization). For purposes of illustration, the test is applied to predictions of ows around the Wigley parabolic hull given by two CFD methods that solve the Euler equations with fully nonlinear boundary conditions at the free surface. is illustrative example dem- onstrates that the test can indeed be useful to identify numerical inaccuracies. e ana- lytical relations can also be used to determine experimental values of the ow velocity at a ship wave prole that correspond to measure- ments of the wave prole. Computational Fluid Dynamics Analysis of the Scavenging Process in the MAN B&W 7S50MC Two- Stroke Marine Diesel Engine BY MARÍA ISABEL LAMAS, RODRÍGUEZ VIDAL, AND CARLOS GERVASIO PUBLISHED IN THE SEPTEMBER JOURNAL OF SHIP RESEARCHis paper focuses on a computational uid dynamics (CFD) analysis to simulate the scav -enging process in the MAN B&W 7S50MC. is is a two-stroke diesel engine with uniow scavenging. In recent years, low-speed, MC type two-stroke engines have become very popular in a huge number of dierent ships. Using the commercial software ANSYS Fluent, the pressure, velocity, and mass fraction elds were obtained, as well as the scaveng- ing eciency. As expected, the results show a swirling movement around the cylinder axis. To validate the numerical model, the in-cyl- inder pressure was successfully compared with experimental measurements, indicat- ing that the proposed CFD approach can simulate the compression/expansion process with a good degree of accuracy. ese results provide interesting information to improve two-stroke engines because the scavenging process plays a crucial role in pollution lev- els, performance, and eciency. Accordingly, the aim of future work is to use this numerical model to improve the design of current large and medium marine engines. Intelligent Quaternion Ship Domains for Spatial Collision Risk Assessment BY NING WANG PUBLISHED IN THE SEPTEMBER JOURNAL OF SHIP RESEARCHIn this article, a novel ship domain model termed intelligent quaternion ship domain (IQSD) has been proposed by eectively con- sidering ship maneuverability and human factors. Unlike previous ship domains, the proposed IQSD is much more dependable and exible for navigators to make decisions. e key characteristics are as follows: 1) the domain size is determined by the quaternion including 4 radii, i.e., fore, aft, starboard, and port, which suciently take factors aecting the domain (i.e., ship maneuverability, speeds and courses, etc.) into account; 2) the domain shape is mod- eled by another parameter k, which makes the IQSD more exible because the ship bound- ary could be not only linear or nonlinear, but also thin or fat; 3) furthermore, the navigator states including skill ability and physical and mental states have been eectively modeled by a fuzzy system, which determines the shape parameter, k. To reasonably relate the IQSD to potential applications, i.e., collision risk assessment, collision avoidance and trajectory planning, etc., a generalized IQSD (GIQSD) with fuzzy boundaries has been developed by using fuzzy sets. As a consequence, the GIQSD would become more practical and convenient for applications because uncertainty and fuzzy information has been merged into the GIQSD. Furthermore, concepts of longitudi- nal and lateral risk based on the GIQSD have been dened to estimate the spatial collision risk (SCR) for ships encountered. Finally, com- prehensive simulations have been conducted on various encounter situations and compar- ative studies with typical ship domains have been intensively analyzed. Simulation results Editors note: The following are abstracts of papers recently presented at SNAME events and/or published in SNAME publications. The paper s can be found at www.sname.org/ sname/mt/featuredabstracts View current and previous issues of Journal of Ship Production and Design and Journal of Ship Research at http://www.sname.org/SNAME/Pubs/Journals1/