1. Data Acquisition Setup

• Model 5512 is ballasted to its dynamic sinkage and trim for Fr = 0.28 and mounted on the tank centerline in the fixed condition. 
• The PMM scotch yoke is adjusted for a 327.2 mm sway amplitude and a maximum heading angle of 10.2°. 
• PMM potentiometers are incorporated in the sway carriage and yaw linkage to track the model maneuvers. 
• Potentiometer cabling is run to onboard amplifiers. 
• The SPIV system is assembled on an automated two-axis (y, z) traverse which slides on the 4 m strongback underneath the PMM carriage in the x-coordinate. 
• The laser and lightsheet optics are arranged to deliver a vertical lightsheet in the (y, z) crossplane. 

• Standoff distance between the lightsheet generator and the measurement area center is 550 mm. 
• The cameras are arranged with equal standoff distances between the enclosures and the measurement area (880 mm), 33° of separation between cameras, and a 22° angle between camera #1 and the tank axis to provide clearance with the model and avoid an extremely shallow angle between camera #2 and the cross plane. 
• A minimum separation angle of 30° between cameras is maintained to ensure good measurement quality. 
• Power, video, and trigger cables are routed through the strongback to the PIV computer onboard the drive carriage. 
• The laser power supplies ride aboard the PMM carriage. 
• A single umbilical for coolant and electronics cables links the power supplies and the laser head. 
• Laser trigger lines also run through the strongback to the drive carriage PIV computer. 
• The SPIV computer is equipped with frame grabbers, a programmable timing unit, a TTL/IO board, and an 8-channel AD board capable of synchronously acquiring analog voltages and PIV recordings. 

• An IIHR-designed and -built PIV synchronizer is used to provide equally-spaced trigger pulses to the SPIV computer in order to acquire PIV recordings at presettable, repeatable phase angles in the pure yaw maneuver. 
• This is achieved as the synchronizer monitors the analog output from the PMM sway potentiometer. 
• When a predetermined voltage corresponding to 45° on the rising side of the sway curve is reached, the synchronizer emits a burst of 32 TTL’s, each having a 200 msec pulse width and a time between triggers of 233 ms. 
• Since the pure yaw motion frequency is f = 0.134 Hz, this enables a SPIV recording every 11.25° equally spaced through one PMM period.  
• The process is then repeated on subsequent PMM cycles.

Pure sway test:

Pure yaw test:

2. Data Acquisition Procedures

• First, the PMM is activated and ten seconds elapse to allow enough time for the motion to reach a steady rate. 
• A digital oscilloscope monitors the sway carriage analog voltage output and the synchronizer triggers. 
• When they are synched-up, the carriage is started and accelerates through 10 m to a constant speed. 
• Data acquisition commences after traveling another 10 m which allows the unsteady free surface and flowfield to develop and reach a state where they are not in transition. 
• Data acquisition occurs at 4.288 Hz for 19sec enabling 80-90 SPIV recordings or about 2.5 recordings per each of the 32 phases in the PMM cycle. 
• At least 100 carriage runs are performed for a given measurement area position to obtain enough recordings at each phase to achieve convergence of the data.
• Convergence is monitored as the data is acquired and data acquisition is typically stopped when the residual in the velocities drops by two orders of magnitude. 
• Data acquisition is completed at several overlapping zones at each x-station in order to piece together a complete picture of the region of interest. 
• Four or five zones are used at each x-station to cover the region of interest.