Vibrationdata Blog

Matlab’s built-in function for Butterworth filtering has stability issues. The following code snippet yields an unstable filter. The cutoff frequency is 4 Hz. The sample rate is 20000 Hz. The filter is a high pass, sixth order. fh=4;sr=20000;order=6;Wn=fh/(sr/2);[bb,aa] = butter(order,Wn,’high’);flag = isstable(bb,aa);if(flag==1)fprintf(‘\n filter is stable… Read more

The aircraft is a De Havilland Canada DHC-3 Otter, Single Engine, Seaplane. It is powered by a Pratt & Whitney R-1340 Wasp, 600 hp, air cooled, radial engine with a propeller hub speed of 2250 rpm (37.5 Hz). This aircraft is used for tours and… Read more

Teeter-Totter, Playground along Riverview Blvd, Kent, Washington State I gave the teeter-totter an initial displacement, without human riders, and recorded the damped sine oscillation with my Android smartphone accelerometer app. The natural frequency was 2.1 Hz with 0.6% damping. The frequency would decrease with riders.… Read more

This rustic bridge is popular with fishermen during the Salmon season from Summer through Fall. The Duwamish supports chinook, coho, chum and steelhead, as well as the more rare sockeye, sea-run cutthroat trout and bull trout. Pink salmon run in the millions every odd-numbered years… Read more

My family and I recently took the Argosy Lock Cruise from Lake Union, through the Hiram M. Chittenden Locks, to the Seattle Waterfront, aboard the Goodtime III. The ship’s main engines are Caterpillar 3408’s coupled with Twin Disc MG514 reduction gears. Auxiliary power is supplied… Read more

This is my current vehicle. With the car parked, I opened the hatch door and sat down on the cargo compartment floor facing outward with my feet on the ground. I then used my legs to move my gluteus maximus up-and-down a few times while… Read more

I recently exercised on the treadmill at Rachel’s Body Shop Gym with an inclination of 3% and a speed of 3.6 mph. I measured the resulting vibration with my Android Smartphone which was mounted against the console screen. My footfall or step frequency was about… Read more

The Green River Bridge is a reinforced concrete structure with an expansion joint on its West end. The joint allows the concrete to naturally expand and contract without cracking as the deck undergoes thermal changes and other loading conditions. Passenger cars have very minor dynamic… Read more

The orange block near the seat post is a Slam Stick X accelerometer. I recorded the frame vibration as I rode the bike over a gravel road adjacent to the Green River in Kent, WA at 10 mph. The time history and power spectral density… Read more

Pedestrian tunnel below Hayden Rd, Scottsdale, Arizona The tunnel is north of Indian School Rd & south of Camelback Rd. It is connected to the Indian Bend Wash which has a series of parks and a golf course along its length. The tunnel is about… Read more