8/3/2019 Disain Peningkatan Kendali Dan Keamanan Kapal Rigid Inflatable Boats (RIBs)_Marine Transport_Townsend_T

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N.Townsend

School of Engineering Sciences, University of Southampton, UK

Influencing the design of rigid inflatable boats (RIBs) to improve ride and safety

The Rigid Inflatable Boat

Model Scale Testing

Acknowledgements

RNLI & EPSRC

FEA Analysis

Summary

Fluid Structure Interactions

Research Group,

School of Engineering

Sciences

In 1962, at Atlantic College in S. Wales, internal floors were added to an inflatable boat in an attempt to improve the boats durability.

This lead to inflatable tubes being glued directly to a rigid floor, by 1963, forming the first RIB.

The RNLI developed the RIB and introduced the first RIB, the Atlantic 21, to service in 1972.The latest RNLI RIB, the Atlantic 85, was introduced to service in 2005.

The distinctive feature of a RIB, the tube, is commented to absorb impacts, providing a smoother ride. However the influence of the tube on themotions of a RIB is not fully understood and there is a need for research to enable engineering justified design improvements to be made.

Drop tests of an Atlantic 85 showed that;

Peak vertical accelerations increase with drop height,

Peak impact pressures increase with drop height, Acceleration signals of drop tests are noisy and include local structural responses, Vertical acceleration signals show a secondary peak value (attributed to the chine impact), The drop height had little effect on acceleration decay time. The response of the tube visually differed with different tube pressures, however no acceleration,

impact pressure or strain showed evidence of the tube pressure having an influence.

Drop tests

Sea Trials

Modal Analysis can be used to determine the naturally occurring vibration frequencies and modal shapes of a system.

Identification of the modal shapes and frequencies, can identify key design parameters.

The analysis found that;

Tube attachment has a greater influence on the modal frequencies than internal pressure and,

Foam tubes have higher modal frequencies than air inflated tubes.

The generally held view that the tube pressure significantly affects a RIBs motion appears to befalse.

Model scale RIB towing tank tests were performed, in regular and irregular head seas, of various heights, periods, speedsand tube pressures.

The motion response of the model RIB to head seas exhibited contouring motion, atslower forward speeds and smaller wave heights and non-linear motion, at greater

speeds and wave heights, figure 1.

Non-linear RIB motions were characterised by higher acceleration, heave and pitchresponses, often including different phases to the encountered waves and of varyingmagnitude.

The tube pressure had no identifiable influence on the motions.

The motions of a RIB are characterised by;

Predominant Z-axis acceleration motion responses, Contouring motion, following the wave profile, at slowspeeds, Non-linear motion responses at speeds approaching planing

and at planing speeds, Frequent slam events (a substantial impact of the hull withthe water surface)

The slam events are characterised by;

Peak accelerations in vertical and horizontal directions (inexcess of 50m/s2),

Peak angular velocities, in roll and pitch directions.

Figure 2: Acceleration Responses

((a): Zero speed (b): At speed (~30knots))

Figure 1: Typical Motion Responses ((a): Contouring motion (b): Non-linear motion)