The two dimensional dynamics of an oil containment barrier, which was designed to have very low tensile loads due to current and waves, were simulated with a theoretical model. The model was solved on both analog and digital computers, and a lab test program conducted to verify the model.
For nonlinear problems such as this, for which "exact" solutions do not exist, the analog computer has many advantages, principally rapid parameter studies and convenient plotting output, plus giving the engineer a real time "feel" for the problem. The problem treated here was especially well suited to analog simulation. Charts and graphs present maximum force and amplitude data, and experimental verification of the solution was obtained from wave tank studies.
In 1970 researchers at Texas A&M undertook the task of designing a light weight mechanical barrier to contain oil spills at sea. Studies indicated that the failure of barriers available at that time was due to current and wave induced tensile loads which, if they did not cause the barrier to tear apart, at least made it impossible for the barrier to adequately follow the ocean surface and prevent oil leakage over or under the barrier.
A typical barrier two feet deep and 1000 feet long will have several thousand pounds tension in a 1-2 knot current. The ability of this barrier to respond to waves is analogous to that of a taut clothesline. Waves will induce structural loads in this barrier nearly as large as those which would be imposed on a fixed structure of the same size and shape. To circumvent these problems, the design depicted in Figure 1 was proposed.
The essential features of the barrier are:
The barrier skirt, which is actually the oil retention portion of the barrier, is separated from a main tension line by bridle lines spaced about every two feet along the main tension line. This separation by many lines guarantees that the current or wave induced tension in the barrier skirt itself will be very small. The dual advantages of this low tension are: first, structural integrity is assured, since the only highly loaded portion of the system is the main tension line (a very efficient load carrying member), and secondly, the low tension allows the barrier to follow every profile and contour in the sea.
The bridle lines are made of elastic shock cords which have the basic mechanics of a rubber band. They allow the barrier to follow with waves coming into the barrier, thus greatly reducing wave-induced forces. The reason for this is that since the relative velocity of the barrier with respect to the sea is much less than with a non-conforming system, the loads in the barrier, which are proportional to the square of this relative velocity are also much smaller.
For a configuration as shown in Figure 1, the tension in the barrier would be on the order of 10 pounds, rather than thousands of pounds.
