Novel technique being explored to warn of impending failures of operational systems

Abstract

When you hear a mysterious new sound when driving your car you know that it usually means trouble. Now such signals can be translated into a “signature” which identifies the problem by a technique called “Random Decrement”. First the vibrations have to be picked up by a sensor, like the pickup in a record player. Then these signals which appear meaningless in their original form are sorted, and a characteristic signature is established which engineers can relate to the mechanical properties of the system. If a flaw such as a fatigue crack develops, the signature changes, thus warning the operator of impending failure. The “Random Decrement” technique is particularly well suited to the class of problems in which characteristics are desired of an in-service structure subjected to unknown random excitation such as wind, earthquakes, waves, sound, traffic loads, etc. Analysis requires only the measurement of the dynamic response of a structure, and not the excitation. Continuous automatic monitoring is possible. The method has been applied in flight flutter testing of the F-16 aircraft, in monitoring the seals during operation of a wind tunnel, in detecting cracks, and measuring damping in structures such as ships, bridges, pipes, and machinery. More recently it is being used in a joint ONR-USGS research program for remote detection of underwater structural failures in ocean platforms.