Control of ship roll and yaw angles during turning motion

In earlier studies we have analyzed the phenomena which can generate loss of ship controllability in astern seas. In this paper we examine how the yaw instability associated with broaching can lead to roll instability and ship capsize. The dynamic effects responsible for capsize during the forced turn of broaching do not have their origin in the customary roll equation but are the result of interactions with other motions of the ship. Stability studies based solely on the roll equation are thus clearly inappropriate for this case where a multidimensional approach is deemed necessary. After presenting the theoretical background we set out a multi-degree method of global analysis which is based on transient maps. We apply this method to clarify how capsize occurs during the escape from surf-riding and also during transients from arbitrary initial condition of the ship. Our study establishes the connection between speed, heading, automatic control parameters and capsize. The proposed method can be useful in the context of a design methodology for minimizing the risk of ship capsize in astern seas.

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Experimental Study on the Stability Performance and Turning Motion of Multi-Connection VAWT

10.1115/omae2021-62662 ◽

2021 ◽

Author(s):

Saika Iwamatsu ◽

Yasunori Nihei ◽

Kazuhiro Iijima ◽

Tomoki Ikoma ◽

Tomoki Komori

Keyword(s):

Scaling Law ◽

Type A ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Water Tank ◽

Type B ◽

Floating Bodies ◽

Stability Performance ◽

Turning Motion ◽

The Stability

Abstract In this study, a series of dedicated water tank tests were conducted in wind and waves to investigate the stability performance and turning motion of Floating Offshore Wind Turbine (FOWT) equipped with two vertical axis wind turbines (VAWT). The FOWT targeted in this study is called Multi-connection VAWT, which is a new type of FOWT moored by Single-Point-Mooring (SPM) system. We designed and manufactured two types of semi-submersible floating bodies. One is a type in which VAWTs are mounted in two places of a right-angled isosceles triangle (Type-A) on a single floater, and the other is two independent units equipped with VAWTs on two separate floaters centered on a moored body. This is a type in which two semi-submersible floating bodies are lined up in a straight line (Type-B). The experimental conditions were determined by scaling down to 1/100 using Froude’s scaling law based on a wind thrust load of 320 kN (rated wind speed of 12 m/s) assuming an actual machine. In the free yawing test in waves, Type-A turned downwards, while Type-B was barely affected by the waves. Furthermore, in the free yawing test in wind, both Type-A and Type-B turned leeward and stabilized at a final point where the wind load was balanced.

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