Abstract

Laboratory tests performed at The University_ of Texas at Austin have shown that a floating offset breakwater configuration can achieve wave transmission coefficients less than 0.2 in both regular and wind waves. The offset configuration consists of vertical reflecting surfaces separated by a distance which is one-half the wave length of incident design waves.

Experiments indicate that the offset break- water provides effective wave attenuation for angles of incidence up to 45 degrees. Therefore, many applications to wave-protection in confused seas are possible. Portability of the floating breakwater permits field adjustment to give the best results. Temporary protection can be provided to construction sites where offshore facilities may be fabricated or installed. Also, the offset configuration can be built into booms for oil slick collection and confinement in heavy seas.

Good motion characterize-tics of the offset configuration encourage many applications to floating structures. A model circular structure for possible use as an offshore supertanker terminal has been tested in the laboratory. An offset configuration is suggested for pipeline lay barges to reduce their down time in rough weather, particularly beam seas.

Introduction

Protection of coastal areas from wave action is commonly achieved by building massive rubble mound structures which are supported by the soil on the bottom. Properly designed, these structures can be effective and permanent, with relatively little maintenance expense. In deep water, however, the first cost becomes very high, inasmuch as the volume of material required increases roughly as the square of water depth.

To provide more economical wave protection in deep water areas, recent interest has focused on floating structures which could be fabricated at inshore locations and towed to the application site. Cost savings result from reduced material requirements and cons traction economies in sheltered areas. Floating structures also have the advantage of portability; they can be moved from one location to another as the need arises. Their main disadvantage is that sizeable mooring forces are often required to hold them in place. These forces may exceed the working capacity of mooring lines or the holding power of anchors, possibly causing a failure in the mooring system. Such a failure could result in heavy damage to or abstraction of the structure.

The offset configuration has been designed with the objective of reducing anchoring force a which are required to hold the floating breakwater in place. Reducing the anchoring forces also implies less structural motion and less wave transmission by wave regeneration. The offset breakwater design has been tested in both regular and wind waves, and it has an even effective in attenuating the heights of both types of waves. Laboratory tests are being continued to obtain experimental misstatements of anchoring force

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