LAB 4 Waves and Wave Induced Currents

Wave_A

Procedure
Video: Wave Measurement
Group Velocity
Video: Standing Wave
Beach Behavior

Introduction

Safety Considerations

  • Stand clear of the rotating disk while the motor is running as the
connecting screw is known to fall off.
  • When running the water hose across the walkway ensure it is laying flat 
across the walking path to minimize the tripping hazard.
  • Never leave power connections (e.g. electrical plugs) on the ground in 
case of flooding
  • Do not operate the machine above the suggested speed

 

 

 

Procedure

Setup

  1. Close the drain on the end of the flume. (Red Tap)
    Wave_B
  2. Use the green hose by the wall to fill the flume with water.
    Wave_C

    Position the green hose as shown above.

  3. Raise or lower the sluice gate to fill the flume with water to ~18cm in depth.


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Video: Wave Measurement

The following video demonstrates how to set the wave paddle and the motor speed. Insert video 1

CIVL 316 Lab4 Video 1: Waves – Standing Wave
  1. Set the wave paddle stroke by moving the paddle-motor arm to the maximum value (¾ of the radius of the stroke adjuster).
  2. Set the motor speed to zero and turn on the motor power.
  3. Increase the frequency gradually until the desired wave height occurs.

    Note: If the frequency was increased by too much, the wave will break before it is properly generated by the paddle. The resulting wave will have a low amplitude and will be irregular. If this happens, reduce the frequency until the wave is properly generated by the paddle.

  4. Measure the wave period T, the wave height H, and the wave speed c. Repeat these measurements 2 to 3 times to make sure a consistent result. Average your readings.
  5. Observe the particle orbits near the water surface and near the bed. Measure the horizontal orbit diameter D of water particles at the water surface and at the bed by using some of the small blue pellets provided.
  6. Choose a new wave frequency and observe the change in wave height. Repeat step 7.
  7. Turn off the paddle and reduce the paddle stroke to about 2/3 of the radius of the stroke adjuster. Repeat steps 5-9. To obtain 2 new frequencies at this stroke setting.
  8. 1Repeat steps 5-9 for a stroke setting of 1/3 of the radius of the stroke adjuster.


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Group Velocity

Ask the T.A. to explain what happens during this part of the experiment. The idea is to obtain a measurement of the group velocity c and compare it with the theoretical equation.

  1. Turn on the motor at low speed and align the arm and the groove on the stroke adjuster, then turn off the motor.
    Wave_D

    The aligned arm forms a straight line with the groove as shown in the picture.

  2. Set the motor speed to 100.
  3. Turn on the motor. After the second wave is emitted immediately reduce wave speed.
  4. Ignore the first wave emitted from the paddle
  5. Measure the wave speed of the second wave. The speed of this wave is the group velocity.
  6. Reduce the motor speed and align the arm with the groove in the stroke adjuster. Then turn off the motor.
  7. Repeat steps 3 – 6 several times to improve your data.


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Video: Standing Wave

The following video demonstrates how to obtain standing waves2

CIVL 315 Lab4 Video 2: Wave Set Wave Speed

A metal plate is provided which can be fitted into the wave flume to act like a vertical sea wall at the beach end of the flume. This plate will reflect the waves, causing a standing wave train to form. Note how the wave amplitude increases.


Wave_E

  1. Turn off the motor. Slide metal “L” under the blue mat to hold it steady.
  2. Set motor speed to zero. Then turn on the motor and slowly increase speed.
  3. Compare the standing wave’s properties with the progressive wave.


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Beach Behavior

Using the maximum stroke and maximum wave height, observe how the waves break on the beach. Observe how the breaking wave erodes the beach and how the sediment moves.

    1. Set the stroke adjuster to maximum distance.
    2. Remove the protective blue mat from the sand.
    3. Set the motor speed to zero. Then turn on the motor and set speed as high as possible while still emitting sinusoidal waves.
Set Motor Speed

Set Motor Speed

  1. Observe how the waves are affecting the beach. They should be wearing the beach down. Sketch your observations.
  2. Set the motor speed to low.
  3. Observe how the waves are affecting the beach. They should be building the beach up. Sketch your observations.
  4. Turn off the motor and replace the protective blue mat.

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