1:45 PM - 3:15 PM
[O11-P43] Construction of wave experiment device and in situ observation of ripple marks
Keywords:Ripple marks, sedimental structure, wave dynamics
1.Introduction…Submarine sedimentary landforms and waves:
Above sandy beach coastlines, ripple marks are often observed. In addition, the waves strength and frequency have much daily varied, making the ripple marks formed each day different from one another. Observe the relationship between the waves and the ripple marks, we can understand the trends of forming ripple marks and can help predict the coastal environments of the geological past based on the sedimentary structures within the layers formed as a result of those environments.
2.Method 1: Development of the Mechanism
Using a motor-driven vibration structure and simple wood materials, we constructed a wave generation experimental device in which the vibrator strikes the water surface.
The mechanism that transmits rotational motion from the motor was based on that of a toy battery-powered buggy. Devices that generate waves can be found in flowing pools and artificial surfing fields, as well as in facilities examining structural testing caused by tsunamis.
However, normal daily waves have short-term caused by wind-blowing currents, we thought it would be needed to strike the water surface in a linear shaped with a short period, thus I considered a mechanism that periodically drops and lifts a reverse T-shaped vibrator at regular intervals.
3.Method 2: Generating Ripple Marks field
Ripple marks are formed at the shoreline from relatively shallow sea-beds. Therefore, the water depth should be shallow enough, and the wavelength of the vibrating wave would be around few centimeters. We used a plastic case with a width of 30 cm was prepared with a water depth of about 30 mm, and the vibrating element was also made to match that size, using lumber measuring 30 cm in length and 15 mm in width. The sand at the bottom was also sorted to be homogeneous with a grain size of 500 µm/250 µm which were using a sieve.
4. Results
The experiments operated by wave experiment device allowed for the realization of various underwater terrains due to differences in the wavelength of the water surface. With a water depth of 30mm, an output of 1.5 to 3V, and one, two or four fins on the vibrating rotor, the frequency at which the water surface was struck was set to 2Hz,4Hz and 8Hz. This led to the observation that the number of ripples left in the sediment increases proportionally with the frequency at which the water surface is struck. Particularly, at 4Hz with a wavelength of about 8cm with 500µm, clear ripple marks with 4 to 5 waves were formed over a length of 20 to 30cm.
Additionally, even at 8Hz with waves of about 4cm on 250µm sands, the rotation and vibration of the sand on the bottom created ripple marks, but the horizontal random vibrations tended to cancel them out them to be engulfed by the backflow of water returning after being pushed out, making it difficult for them to remain as distinct ripple marks.
Currently, we are conducting a quantitative comparison of wave numbers and the formed ripple marks and continuing examining the sandy texture. We would like to discuss on that day.
Above sandy beach coastlines, ripple marks are often observed. In addition, the waves strength and frequency have much daily varied, making the ripple marks formed each day different from one another. Observe the relationship between the waves and the ripple marks, we can understand the trends of forming ripple marks and can help predict the coastal environments of the geological past based on the sedimentary structures within the layers formed as a result of those environments.
2.Method 1: Development of the Mechanism
Using a motor-driven vibration structure and simple wood materials, we constructed a wave generation experimental device in which the vibrator strikes the water surface.
The mechanism that transmits rotational motion from the motor was based on that of a toy battery-powered buggy. Devices that generate waves can be found in flowing pools and artificial surfing fields, as well as in facilities examining structural testing caused by tsunamis.
However, normal daily waves have short-term caused by wind-blowing currents, we thought it would be needed to strike the water surface in a linear shaped with a short period, thus I considered a mechanism that periodically drops and lifts a reverse T-shaped vibrator at regular intervals.
3.Method 2: Generating Ripple Marks field
Ripple marks are formed at the shoreline from relatively shallow sea-beds. Therefore, the water depth should be shallow enough, and the wavelength of the vibrating wave would be around few centimeters. We used a plastic case with a width of 30 cm was prepared with a water depth of about 30 mm, and the vibrating element was also made to match that size, using lumber measuring 30 cm in length and 15 mm in width. The sand at the bottom was also sorted to be homogeneous with a grain size of 500 µm/250 µm which were using a sieve.
4. Results
The experiments operated by wave experiment device allowed for the realization of various underwater terrains due to differences in the wavelength of the water surface. With a water depth of 30mm, an output of 1.5 to 3V, and one, two or four fins on the vibrating rotor, the frequency at which the water surface was struck was set to 2Hz,4Hz and 8Hz. This led to the observation that the number of ripples left in the sediment increases proportionally with the frequency at which the water surface is struck. Particularly, at 4Hz with a wavelength of about 8cm with 500µm, clear ripple marks with 4 to 5 waves were formed over a length of 20 to 30cm.
Additionally, even at 8Hz with waves of about 4cm on 250µm sands, the rotation and vibration of the sand on the bottom created ripple marks, but the horizontal random vibrations tended to cancel them out them to be engulfed by the backflow of water returning after being pushed out, making it difficult for them to remain as distinct ripple marks.
Currently, we are conducting a quantitative comparison of wave numbers and the formed ripple marks and continuing examining the sandy texture. We would like to discuss on that day.