Experimental Investigation of Propeller Wake Wash

在冰雪覆盖的水域航行要求船舶能够在自然冰条件下运行，如破碎的浮冰和完整的水平冰。传统的破冰作业主要依靠船只的质量和动力来破冰。船的结构必须相应地坚固。船舶推进技术的最新创新为利用螺旋桨尾流作为另一种破冰、清冰和管理冰的手段提供了机会。采用螺旋桨尾流的破冰作业可以显著减少传统破冰作业中涉及的船舶结构与冰的相互作用，从而降低结构损坏和燃料或货物意外泄漏的可能性，并提高作业的能源效率。多年来，水手们一直使用螺旋桨尾流来清除航道上的碎冰，但直到方位角推进器出现后，它才被设计成一种操作方式。目前，由于对尾流如何在螺旋桨下游发展并随后与自由海面海冰相互作用的基本了解有限，因此设计是在临时基础上完成的。拟议的研究将解决这一知识差距。

Navigation in ice-covered waters requires that vessels be capable of operating in natural ice conditions, such as broken pack ice and intact level ice. Conventional ice-breaking operations rely largely on the mass and power of the vessel to break through ice. The ship's structure must be correspondingly strong. Recent innovations in marine propulsion technology have provided opportunities to use propeller wake wash as another means to break, clear, and otherwise manage ice. Icebreaking operations employing propeller wake wash can reduce significantly the ship structure-ice interaction involved in conventional icebreaking, thereby reducing the likelihood of structural damage and accidental spills of fuel or cargo, and improving the operation’s energy efficiency. Propeller wake wash has been used for years by mariners to clear broken ice from shipping channels, but it has only been since the advent of azimuthing types of propulsors that it has been incorporated into operations by design. At present, the design is done on an ad hoc basis as there is limited fundamental understanding of how the wake wash develops downstream of the propeller and subsequently interacts with sea ice at the free surface. The proposed research will address this knowledge gap. The proposed research will characterize propeller wake wash in terms of the 3-D fluid velocity field downstream, including the velocity field at the free surface. The characterization will be based on laboratory experiments. Experiments will be done in the tow tank at Memorial University's Ocean Engineering Research Centre. Experiments will focus first on the propeller wake wash in the absence of ice, and then on the interactions of the wake wash and ice. The focus of interest in terms of ice features will be on pack ice. A semi-empirical mathematical model will be developed of the downstream wake, and the interaction between the flow at the free surface and its interaction with pack ice. The model of the wake wash field will include mean velocities, as well as of its variability throughout the downstream wake. It will be tested against field observations of ships in ice, as the final experimental element of the proposed work. The wake model will predict the downstream surface velocity field in terms of key factors: delivered power, depth of submergence of the propeller, and inclination angle of the propeller to the free surface. When coupled to the ice interaction model, the model should predict how wake wash can clear pack ice en masse downstream from the propeller. This will be useful for designers and operators, such as commercial shipping, the Coast Guard, Navy and others who navigate in ice in connection with transportation, exploration and defense. The proposed research covers a 5 year time span. Four Master’s students will work on this program. All graduate students will be in a thesis-based degree program.