Slide 1

Disdrometer Love Rain on My Parade By Josh Molzan Steve Gronstal Slide 2 What the Heck is a Disdrometer An instrument to measure the drop size distribution falling hydrometeors Three main types: Video disdrometers Acoustic disdrometers Impact disdrometers Slide 3 An Impact Detector Momentum transferred: P = Mass * Velocity Mass = f(size) Velocity = f(size) Basically, Size is EVERYTHING Slide 4 Creating Our Disdrometer Slide 5 Our Disdrometers Slide 6 The piezoelectric device: What is it and how does it work? Piezoelectricity is the ability of some materials to generate an electric field or electric potential in response to an applied mechanical stress. Basically, the harder you push it, the bigger the voltage. Slide 7 But its sooo small Is the detector big enough to accurately measure the rainfall distribution? Slide 8 Rainfall Rate Slide 9 How many drops hit per second? Slide 10 So how many drops hit? Rainfall Intensity Rainfall Rate (mm/hr) Average Diameter (mm) Detector Area (mm 2 ) Hits (#/s) Light< 2.5 mm/hr1.012571.33 Moderate2.5 - 10 mm/hr1.512570.99 Heavy10-50 mm/hr2.012572.08 Slide 11 Experiment 1 Examining the signal of a drop on each sensor Slide 12 The Good (Head 3) Slide 13 The Bad Slide 14 The Ugly (Head 1) Slide 15 Analyze lots of drops per detector Slide 16 Experiment 1: Results PeaksOscillation PeriodDecay RateAmplitude (V) Per EventStDevAverageSt. DevAverageSt. DevAverageSt. Dev Percent Deviation Head 1135.818182155.7704973.4911920.6691990.0480310.079475-0.3128160.561897-179.63 Head 231.64705912.5042603.9638840.5604680.0373970.028595-1.2268790.289811-23.62 Head 331.4761904.3774315.1208940.1141210.0216970.005515-1.7974580.207548-11.55 Head 4Failed Head 532.5000009.0428272.4619760.2464960.0226830.003937-0.7281570.306096-42.04 Head 631.6666674.7791825.8225520.1167790.0211190.003954-1.8223220.126192-6.92 Head 7Failed Head 8Failed Slide 17 Experiment 2 Examine how much size matters. Drop 4 different size drops onto our favorite detectors. Find the relationship between Voltage response and drop size. Slide 18 Creating Drops Head Fall Height (cm) Diameter (mm) Mass/ Drop (mg) Estimated Velocity (m/s) Terminal Velocity (m/s) 25G166.02.387.0854.3567.26 21G165.82.8612.2404.7107.85 18G168.33.5523.4005.1428.57 Buret181.54.5549.3655.4129.02 Slide 19 This Signals (H3, Buret) Slide 20 Analyzing the Signal Damped Harmonic Oscillator (i.e. a spring) Slide 21 Results. But What does it mean? PeaksPeriodDecayAmplitudeVoltage Offset Head Drop MassAverageSt.Dev.AverageSt.Dev.AverageSt.Dev.AverageSt.Dev.AverageSt.Dev. 37.08517.063.3167.4631.47670.0050650.00155-1.120.1190.11580.03371 312.24016.502.71016.0905.92110.0041620.000925-1.400.1390.15690.02095 323.30517.943.49018.7085.63370.0048380.000938-2.040.0950.19820.01894 349.36538.264.34834.5254.18160.0036990.000384-7.860.012-0.04150.01222 67.08521.605.40010.6673.60000.0070380.001653-1.490.2980.06350.01683 612.24018.943.72518.2834.56050.0076260.001581-2.570.2680.00750.02701 623.30515.322.59320.9385.64110.0078750.001468-3.390.4550.06590.05093 649.36539.943.24724.2082.40570.0060650.000394-7.820.016-0.08810.01578 Slide 22 Voltage Relationships? Possibility One: Model our system using Electrical Potential Energy V KE? Possibility Two: Model our system as a spring. V 2 KE Slide 23 Electric Potential Energy Assumptions The KE of the raindrop is completely transferred to the detector The initial KE is then converted into Electric Potential Energy. The Voltage Change acts like a pt charge moving in an electric field. Slide 24 Is V KE?? Slide 25 Energy of a Spring Assumptions The KE of the raindrop is completely transferred to the detector The initial KE is then converted into Spring Potential Energy. For Piezoelectric materials, a change in stress results in a change in potential Capacitors have the same relationship! Slide 26 Is V 2 KE?? Slide 27 Log D vs Log A Slide 28 Diameter 3 vs Amplitude 2 Slide 29 Conclusion After analyzing 250,000,000 lines of data, our results indicate Kinetic Energy is proportional to Potential Squared. More data points are needed to confirm the relationship between particle diameter and voltage response! With more work, a piezoelectric transducer will make a decent disdrometer. Slide 30 Future work to do: Experiment with smaller drop sizes (< 2mm diameter). Experiment with drops at terminal velocity. Experiment with an oscilloscope that can handle larger voltages. Determine the voltage variation due to drop impact location. Move analysis to real-time..