Six-Degree-of-Freedom Sensor Fish Design and Instrumentation

Fish passing through dams may be injured or killed despite advances in turbine design, project operations and other fish bypass systems. The six-degree-of-freedom (6DOF) Sensor Fish device is an autonomous sensor package that characterizes the physical conditions and physical stresses to which fish are exposed when they pass through complex hydraulic environments. It has been used to identify the locations and operations where conditions are severe enough to injure or kill fish. During the design process, a set of governing equations of motion for the Sensor Fish was derived and simulated to understand the design implications of instrument selection and placement within the body of the device. The Sensor Fish package includes three rotation sensors, three acceleration sensors, a pressure sensor, and a temperature sensor with a sampling frequency of 2,000 Hz. Its housing is constructed of clear polycarbonate plastic. It is 24.5 mm in diameter and 90 mm in length and weighs about 43 g, similar to the size and density of a yearling salmon smolt. The accuracy of the pressure sensor was determined to be within 0.2 psi. In laboratory acceptance tests, the relative errors of both the linear acceleration and angular velocity measurements were determined to be less than 5%. An exposure is defined as a significant event when the acceleration reaches predefined thresholds. Based on the different characteristic of acceleration and rotation velocities, the exposure event is categorized as either a collision between the Sensor Fish and a solid structure or shear caused by turbulence. Since its development in 2005, the 6DOF Sensor Fish has been deployed successfully at many major dams in the United States.