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ABSTRACTThis paper investigates a coupled computational fluid dynamics (CFD)/potential propeller code approach to simulate maneuvers of ships. While this approach is successful in submarines, the concept has not been evaluated before for cases where an object (the rudder) is immersed in the wake. The study uses the CFD code REX and the propeller code PUF-14 applied to propeller/rudder interactions in open water configuration and to a 15/1 zigzag maneuver for the KCS container ship. Self-propulsion results, and motions, forces, moments and mean flow field during the maneuver agree well with experiments and discretized propeller simulations. The approach is an effective and economical way to perform direct simulation of surface ship maneuvers, providing CPU time savings approaching an order of magnitude. Massively separated rudder flows may not perform as well, since the propeller turbulence reaching the rudder is under-predicted in the coupled approach.

Elevated levels of dissolved gas in the spillway stilling basin, which are responsible for gas bubble disease in fish, constitute an important negative environmental effect of dams. Bubbles, entrained when a plunging jet impacts the tailwater pool, plunge beneath the surface and transfer mass to the liquid, causing an increase in the total dissolved gas (TDG) concentration. Most of the numerical studies onTDG downstream of spillways found in the literature are based on experimental correlations for the gas volume fraction.Abetter approach involves the use of a two-phase flowmodel. In this paper, a two-fluid model is used to calculate the gas volume fraction and velocity of the bubbles. A polydisperse model is used in which a Boltzmann transport equation predicts the bubble size distribution, to account for the different bubble sizes found in the flow downstream of spillways. The bubble mass is discretized considering groups of bubbles of variable mass, with the mass of the bubbles changing due to bubble/liquid mass transfer and pressure. A two-phase transport equation for the TDG is presented, whose source is the bubble/liquid mass transfer, which is a function of the gas volume fraction and bubble size distribution. Two-dimensional numerical results of TDG, gas volume fraction, bubble number density, and velocities are presented and discussed. The predictions of TDG downstream of a spillway are compared against field data in the stilling basin ofWanapum Dam, on the Columbia River.

Abstract: Steady flow simulations for the Korean Research Institute for Ships and Ocean Engineering (KRISO) container ship (KCS) were performed for towing and self-propulsion. The main focus in the present article is on the evaluation of computational fluid dynamics (CFD) as a tool for hull form design along with application of state-of-the-art technology in the flow simulations. Two Reynolds-averaged Navier-Stokes (RANS) equation solvers were employed, namely CFDShip-Iowa version 4 and Flowpack version 2004e, for the towing and self-propulsion cases, respectively. The new features of CFDShip-Iowa version 4 include a single-phase level-set method to model the free surface and an overset gridding capability to increase resolution in the flow and wave fields. The new features of Flowpack version 2004e are related to a self-propulsion scheme in which the RANS solver is coupled with a propeller performance program based on the infinitely bladed propeller theory. The present work is based on a close interaction between IIHR-Hydroscience and Engineering of the University of Iowa and Osaka Prefecture University. In the following article, overviews are given of the present numerical methods and results are presented and discussed for the KCS in towing and self-propulsion modes, including comparison with available experimental fluid dynamics (EFD) data. Additional evaluation is provided through discussion of the recent CFD Workshop Tokyo 2005, where both methods appeared to yield very promising results.