Evaluation Method of Remaining Oil Properties in a Sunken Ship Using Ultrasonic Technique

The object of this paper is to clarify the ultrasonic estimation method for oil properties which is necessary for recovery from a sunken ship. We examined numerical relation between oil properties and ultrasonic propagation characteristics and introduced numerical formulas which calculate ultrasonic attenuation and reflection coefficients at a tank wall-oil boundary using oil properties. Ultrasonic attenuation is closely related with viscosity and we evaluated their calculated attenuation in various types of oil from a point of measurement at a sunken ship. The most oil assumed in a sunken ship shows quite high attenuation and a measurement of ultrasonic attenuation and velocity is found to be impractical to a sunken ship. As an applicable measurement method to a sunken ship, we investigated on ultrasonic reflection phenomenon at steel-oil interface affected by oil viscosity. In case of shear wave, the reflection coefficient is largely dependent on oil viscosity, and the reflection measurement shows some possibility to viscosity estimation. In case of longitudinal wave, the reflection coefficient is found to be largely dependent on oil density and bulk modulus, are almost free from oil viscosity.