Scientists break new ground with wave theory for sea defencesWaves crashing violently on the seashore may look spectacular, but the continuous battering of harbour walls, jetties and sea defences can take its toll on the structure. And as every wave is unique, it's impossible to predict the long-term effects of repeated violent waves on, say, a sea wall. So how can you maintain and repair structures that are constantly pounded by waves if you don't understand how or what damage is being done? Researchers in the School of Mathematics at the University of East Anglia are teaming up with engineers from all over the world to try and come up with a solution. Waves can exert pressures of up to 10 tonnes on a square metre of a wall. But despite causing this huge pressure, they last only a fraction of a second. This makes it difficult to make any measurements in the wave and on the surface of the wall at the point of impact. To make things even more complicated, debris lying on the sea bed and cracks in the wall will also affect the behaviour of the wave. So engineers use artificial "wave tanks" to try and mimic the complicated real-life situation in the laboratory. Using this method, researchers have explored what happens in cracks in the surface of a wall. No-one has known until recently how these might influence the effect of the wave hitting the wall. Researchers at UEA and Queen's University Belfast have found that tiny air bubbles in the water inside deep crevices may reduce the pressure of the impacting wave deep inside the structure. So this must be accounted for in all the theoretical calculations of the effects of waves, as most real-life situations involve water which contains lots of air bubbles. This work can be applied in a variety of ways. For example, it may be useful in helping to advise on maintenance strategies for existing sea defences. Many of these are Victorian, so are in need of repair. In some cases (such as in the Peterhead Breakwater in Scotland), the mortar between the concrete blocks has been washed away. This has left deep cracks in the wall. Should these cracks be filled, or are they serving a useful purpose in helping to reduce the pressure deep in the wall exerted by the waves? This is one question that the UEA mathematicians hope to address using their ideas and calculations. Another application is helping to explain the failure of sea defences. Often, (such as at Overstrand in North Norfolk), blocks of granite are placed at the bottom of cliffs to help absorb the huge energy from the waves before it hits the cliffs. However, this strategy doesn't always work, for reasons that aren't fully understood. The UEA researchers hope that by understanding what causes the blocks to break up in some cases but not others could go some way to help improve sea defences. One of the benefits of applying mathematics to these problems is
that it is relatively inexpensive. Collaborations between mathematicians
and coastal engineers will hopefully improve out practical understanding
of sea walls and protect us better from the ravages of the sea. © Dr Belinda Clarke 2001 This Article originally appeared as part of the "Science on your Doorstep" series, published in the Eastern Daily Press 3rd February 2001
NRP
Partners
|
