• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.25-29
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• 2016

The high temperature superconducting (HTS) contra-rotating propulsion (CRP) systems comprise two coaxial propellers sited on behind the other and rotate in opposite directions. They have the hydrodynamic advantage of recovering the slipstream rotational energy which would otherwise be lost to a conventional single-screw system. However, the cooling systems used for HTS CRP system need a high cooling power enough to maintain a low temperature of 2G HTS material operating at liquid neon (LNe) temperature (24.5 - 27 K). In this paper, a single thermo-syphon cooling approach using a Gifford-McMahon (G-M) cryo-cooler is presented. First, an optimal thermal design of a 1.5 MW HTS motor was conducted varying to different types of commercial 2G HTS tapes. Then, a mono-cryogenic cooling system for an integration of two 1.5 MW HTS motors will be designed and analyzed. Finally, the 3D finite element analysis (FEA) simulation of thermal characteristics was also performed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.1 no.1
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• pp.29-38
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• 2009

A ship's screw-propeller produces thrust by rotation and, at the same time, generates rotational flow behind the propeller. This rotational flow has no contribution to the generation of thrust, but instead produces energy loss. By recovering part of the lost energy in the rotational flow, therefore, it is possible to improve the propulsion efficiency. The contra-rotating propeller (CRP) system is the representing example of such devices. Unfortunately, however, neither a design method nor a full-scale performance prediction procedure for the CRP system has been well established yet. The authors have long performed studies on the CRP system, and some of the results from the authors' studies shall be presented and discussed.

• Bulletin of the Society of Naval Architects of Korea
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• v.4 no.1
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• pp.59-65
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• 1967

Since the screw propellers were adopted as ship propulsion devices, the replacement of propeller shaft due to damage was mostly of fatigue failure due to the alternative stresses [1],[2]. To prevent such a failure, hence, it is suggested that careful attention should be paid to account of the alternative stresses on the design stage of the propeller shafts. In connection with this fact the Ship Classification Societies' Rules are regarded simply as guidance for preliminary determination of the shaft diameter. In this paper, limiting the topic to the small and medium-sized motor ships, an evaluation of the Rules formulae to a theoretical based on Soderberg's correlation [5] between the factor of safety and the resultant stresses obtained by application of the maximum shear theory is done. For this purpose eleven (11) ships built recently in Korea were taken as a species(refer to table 2. in text). In the end the following conclusions are made: (1) In general the Rules formulae give considerably larger size of the propeller shaft diameter than that derived from theoretical calculation, that is, about 7% more in AB and BV Rules, and about 20% more in LR and KR-NK Rules. (2) LR Rule gives the largest size of all, and AB Rule is mostly closed value to the theoretical. (3) The formular of the AB Rule is considered to be of the simplest in utilization and of the reasonable.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.7
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• pp.927-935
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• 2019

Screw-failure accidents in small ships frequently occur in coastal waters. In particular, vessels' propulsion systems are frequently coiled due to objects such as fish-nets and ropes that float on the sea. The failure of the ship's propulsion system can cause primary accidents such as ship operation delays and drifting due to loss of power; furthermore, the possibility of secondary accidents such as those involving operators in the underwater removal of rope stuck in a propeller. Ships that do not have the proper tools to solve these problems must be either lifted onto land to be repaired or divers must dive directly under the ship to solve the problem. Accordingly, some small vessels have been equipped with rope-cutter devices on the propeller shaft to prevent ship propeller system accidents in recent years; however, they are not being applied efficiently due to the cost and time of installation. To solve these problems, this study develops an underwater rope-cutter device and controller for the removal of propeller and shaft foreign material in small vessels. This device has simple structures that use the principle of a saw. Meteor gears and crank pins were used for the straight-line rotation of saw blades of the underwater rope-cutters to allow for long strokes. Furthermore, the underwater rope-cutting machines can be operated by being connected to the ship battery. The user, a non-professional, can ensure convenience and stability by applying reverse current prevention and a speed control circuit so that it can be used more conveniently and safely.