China
Africa
Explore chapters and articles related to this topic
20th Century Engineering — Part 2
Published in Ervan Garrison, A History of Engineering and Technology Artful Methods, 2018
In materials the greatest change has been in the use of high tensile steels in hulls which has been significantly reduced due to corrosion control costs and consequent reduced use lives of hulls.49 Hulls now contain as much as 65% mild steel.50 Other factors contributing to the technological evolution of the modern ship hark back to propeller and hull forms that had only been found in museums. While promising in the past these concepts did not achieve full-scale application because fuel was too cheap to make their adoption worthwhile.51 Naval engineers and architects have revisited these earlier ideas. One such idea is paired contrarotating propellers (CRP) which have been reported to realize a 14% increase in efficiency.52 This two propeller system consists of the units being in tandem on a shaft driven in reverse of each other. The front propeller generates rotational flow that it does not effecively use channeling it to the aft propeller which recovers the energy into an effective force.53 The CRP concept dates back to 1826 but has been “rediscovered”.54
Shaft Engines
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
Contra-rotating propellers, also referred to as coaxial contra-rotating propellers or high-speed propellers, apply the maximum power of an engine (or engines) to drive two propellers one behind the other about the same axis in opposite directions.
Enhancing the roll dynamics of an AUV by contra-rotating-propellers
Published in Ships and Offshore Structures, 2021
Mohsen Ebrahimi, Ahmad Kamali, Madjid Abbaspour
A contra-rotating propellers system consists of a pair of propellers that are coaxial and rotating in the opposite direction. This system, mainly used as a propulsion system, has proper advantages such as high efficiency under high loads, low reaction torque, high maximum thrust power for a given diameter (Štorch 2017). The purpose of this paper is to study the roll control capability of the contra-rotating propellers system. At first, the roll dynamics of a Remus AUV using a single propeller system is investigated by developing a dynamics simulator. It is followed by developing the control system simulator and evaluations of using a contra-rotating propellers system as a roll control strategy.