Computer Design for Particle Image Velocimetry
Ben Falconer
Particle Image VelocimetryUsed to measure the velocity
of a flow field cross sectionLaser creates a light sheet
through the flowCameras take quick series of
imagesCorrelation yields velocities
Multiple cross sections create a 3D map of the flow field
Image courtesy of LaVision
The ProjectSymphonyMeasure flow from a jet
engineTwo sides to project
MechanicalDigital
Focus on the digital side
RequirementsControl:
3 high resolution cameras2 lasersOne 2D traverse
Retrieve images from cameras10 images per second
Use Qinetiq’s Noise Test Facility
ProblemsObvious issues
Hostile conditionsLess obvious issues
Large amount of dataHigh acquisition rateLimited hardware
ProblemsHostile conditionsVibrations
High frequency and low frequency
Very hotAround 850K in the centre
Controlled from ~400m awayNo one is allowed in the test
chamber during experiments
ProblemsLarge amount of data
192GiB per run2048 × 2048 pixel 8 bit frames1000 double frames in each position48 positions
Cannot use conventional hard drives close to camerasToo much vibration
Currently large solid state drives (SSDs) are expensive£1150 for a 512GB SSDReasonable prices for 32-64GB SSDs
ProblemsHigh acquisition rate
Capturing frames at 10Hz40MiB/s
Maximum speed of Gigabit Ethernet is 125 MB/sOverheads reduce this to around 80MB/sToo slow to transfer multiple images simultaneously10 Gigabit exists but is extremely expensive
Hard drive speeds around 70 MB/sAgain too slow to write multiple images simultaneously
ProblemsLimited hardwarePCO cameras
Proprietary cables ~4m longInterfaces with PCI card
Hard drivesSlowVulnerable to vibration
LasersNeed local triggering
Network Design
Network DesignDriving the devices
Trigger BoxUsed to synchronise the cameras and lasersAccurate to the nanosecond scale
Solid State Based ComputersAre not affected by vibrationsCannot be far from cameras due to cable lengthDo not have capacity to store images long termAlso used to control traverse
Network Design
Network DesignStoring the data
Backup ServersRAID5 based
Redundancy Good usage of disk space ~3.5TB per server
Placed at ground level away from serious vibrationDedicated Gigabit Ethernet for each server
Only enough bandwidth for one camera’s images each
Network Design
Network DesignManaging the Network
Ethernet to each computerSeparate to data transfer lines
Control TerminalPlaced in control roomRemote desktop used to access other computersAlso used for monitoring other computers
Network Design
ResultsWorking well with single camera, SSD computer, and
backup serverWaiting for shipment of components to build full system
Questions?