On the numerical prediction of seakeeping and of structural loads of high-speed vessels George Zaraphonitis * , Apostolos Papanikolaou National Technical University of Athens-Ship Design Laboratory, Zografou 15773, Athens, Greece Abstract The applicability of an efficient 3D numerical method for the evaluatfion of the seakeeping performance and structural loads of advanced high- speed vessels is investigated. A semi-empirical approach to account for the viscous flow effects on ship’s behavior at speed is presented and discussed. Numerical results are compared with model tests for two high-speed monohull vessels with satisfactory agreement. q 2005 Published by Elsevier Ltd. 1. Introduction The introduction of large high-speed car/passenger vessels in the early 90s confronted the Naval Architects with a series of scientific challenges and technical problems. Among them, one of the most serious appears to be the design of a ship’s structure of adequate strength and stiffness to withstand the worst foreseeable excitation during the vessel’s lifetime and at the same time of reduced weight to enable a high service speed with reasonable propulsive power. This is a quite demanding and complex technical problem, encompassing both a thorough analysis of ship’s hydrodynamics and of structural design. Structural analysis techniques have been applied for years to the design of ship structures and adequate numerical tools are now-a-days available. It seems, however, that the weak point of the applied procedures to high-speed vessels is the proper prediction of the vessel’s responses in typical operational and extreme seaways and the calculation of the resulting structural loads. The today available numerical procedures range from the well-known and widely used strip theory-like methods (as frequency domain [13] or time domain non-linear techniques [3]), to the fully three-dimensional panel and CFD methods (again as frequency [2,5] or non-linear time domain techniques [7,9]). Strip theory is known to be a simple, fast, yet robust and reliable method for the seakeeping analysis of conventional vessels, particularly of low to moderate speed. It is in use in various versions for more than 40 years and results from its application were found surprisingly accurate, even in cases well outside the theoretical range of validity of the method. However, when applied to the evaluation of high-speed vessels (operating at Froude number exceeding 0.50), the results are less satisfactory. At the other end of the range, regarding complexity and theoretical consistency, fully three-dimen- sional numerical methods and relevant codes were developed by use of either ship-bound translating-pulsating Green sources or of simple Rankine sources distributed over the boundaries of the fluid’s domain. These methods aimed to provide accurate numerical predictions of the seakeeping performance of marine vessels, even at high speeds. The practical experience from their use, however, has shown that despite their theoretical consistency, these modern and demanding methods fail to meet, in many practical cases, the highly set expectations, especially when applied to vessels in the semi-displacement mode of operation, often resulting in worst predictions than strip theory codes. Therefore, despite all recent progress in CFD and panel methods, it may be stated that for higher Froude numbers we are still in lack of reliable, robust and versatile software tools for the numerical analysis of a vessel’s seakeeping performance and of the structural wave-induced loading. Acknowledging the importance of the above problem and the urgent need of reliable and robust procedures for the hydrodynamic analysis of modern high-speed vessels, a comprehensive research project (WAVELOADS—‘advanced method to predict wave induced loads for high speed ships’) has been carried with the financial support of the European Union. Among the goals of WAVELOADS was the validation and further development of software tools available in the project’s partnership. One of these tools is NEWDRIFT, developed by the Ship Design Laboratory of the National Technical University of Athens. NEWDRIFT stands some- where in the middle between the traditional strip theory Applied Ocean Research 26 (2004) 274–287 www.elsevier.com/locate/apor 0141-1187/$ - see front matter q 2005 Published by Elsevier Ltd. doi:10.1016/j.apor.2005.08.005 * Corresponding author.