Presentation Information
[O12-P66]Development and Quantitative Analysis of a Low-Cost Wave Ripples Experimental Apparatus
*Ryogo OTAGIRI1 (1. CHUO UNIVERSITY JUNIOR AND SENIOR HIGH SCHOOL)
Keywords:
Wave ripples,Ripple Symmetry Index,Frequency,Quantification
1. Background and Purpose
Ripple marks (hereafter RMs) are sedimentary structures formed when sand is moved and deposited by water flow or wind in the field of earth science. However, previous experimental studies have often focused on describing the shapes of RMs qualitatively, with limited numerical analysis and only a small number of frequency conditions tested. In addition, existing experimental devices for generating waves are typically large and expensive. Thus, the purpose of this study is to construct a low-cost wave-generating device and to quantitatively analyze RMs formed under varying frequencies using this device.
2. Methods
RMs vary in shape depending on the type of wave. They are broadly classified into two types: current ripples formed by progressive waves and wave ripples formed by standing waves. This study focuses on wave ripples (hereafter WRs).
To generate WRs, waves were produced by the reciprocating motion of a carriage driven by a motor. A crank mechanism was connected to the motor to convert rotational motion into reciprocating motion. In this study, a connecting rod was made using LEGO, and a sliding rail was constructed using wooden rods (Fig. 1).
To quantitatively evaluate WRs, the Ripple Symmetry Index(RSI) was used. Previous studies proposed RI and RSI to distinguish between wave ripples and current ripples. According to reviews by Reineck and Singh (1973) and Collinson and Thompson (1982), ripples with RSI ≦ 2.5 are classified as wave ripples, while those with RSI ≧ 3.0 are classified as current ripples. RSI is defined as:
RSI = Ls / Ll
where Ls is the length of the upstream slope and Ll is the length of the downstream slope of a ripple.
In this study, since RMs were generated by reciprocating motion, it was assumed that only WRs would form. To examine how WRs vary under different conditions, frequency was used as a parameter.
The experimental procedure was as follows. Container A (transparent; inner dimensions: width 4.9 cm x depth 25.5 cm x height 17 cm) was placed on a non-slip sheet. Sand sieved to a grain size of #250–500 was added to a thickness of 1 cm, and water was added to a depth of 3 cm. The motor was operated for 5 minutes, and the upstream and downstream lengths of the formed WRs were measured. The motor side was defined as upstream. The experiment was recorded for 5 minutes while the motor was running. A 10-second segment from the recorded video was used to calculate frequency. Steps 1-4 were repeated while changing the motor output.
3. Results
By varying the motor output, clear ripple marks were formed at frequencies between 1.0 Hz and 2.8 Hz. Results obtained under nine different motor output conditions are shown in Fig. 2 and 3.
4. Discussion
The results demonstrate that model experiments of WRs can be conducted by varying frequency. All measured values fell within the RSI range of wave ripples, supporting the initial assumption.
However, the experimental setup had limitations. The narrow width of the tank restricted lateral flow, resulting in flow primarily in one direction and making it difficult to reproduce complex natural flows such as wind or river currents. Additionally, only a single type and grain size of sand was used, rather than mixed sediments. These factors present challenges in accurately reproducing WRs.
5. Future Work
It was observed that even at the same frequency, different motor outputs produced different ripple forms. Therefore, future work will involve more precise measurements and systematic recording of ripple characteristics. Furthermore, frequencies below 1.0 Hz and above 2.8 Hz, where clear ripples were not formed, will be tested using a container with greater depth to enable further quantification.
Since this study was conducted under specific conditions, it does not fully represent natural environments. Future experiments will vary parameters such as grain size and water depth to expand the range of experimental conditions.
Ripple marks (hereafter RMs) are sedimentary structures formed when sand is moved and deposited by water flow or wind in the field of earth science. However, previous experimental studies have often focused on describing the shapes of RMs qualitatively, with limited numerical analysis and only a small number of frequency conditions tested. In addition, existing experimental devices for generating waves are typically large and expensive. Thus, the purpose of this study is to construct a low-cost wave-generating device and to quantitatively analyze RMs formed under varying frequencies using this device.
2. Methods
RMs vary in shape depending on the type of wave. They are broadly classified into two types: current ripples formed by progressive waves and wave ripples formed by standing waves. This study focuses on wave ripples (hereafter WRs).
To generate WRs, waves were produced by the reciprocating motion of a carriage driven by a motor. A crank mechanism was connected to the motor to convert rotational motion into reciprocating motion. In this study, a connecting rod was made using LEGO, and a sliding rail was constructed using wooden rods (Fig. 1).
To quantitatively evaluate WRs, the Ripple Symmetry Index(RSI) was used. Previous studies proposed RI and RSI to distinguish between wave ripples and current ripples. According to reviews by Reineck and Singh (1973) and Collinson and Thompson (1982), ripples with RSI ≦ 2.5 are classified as wave ripples, while those with RSI ≧ 3.0 are classified as current ripples. RSI is defined as:
RSI = Ls / Ll
where Ls is the length of the upstream slope and Ll is the length of the downstream slope of a ripple.
In this study, since RMs were generated by reciprocating motion, it was assumed that only WRs would form. To examine how WRs vary under different conditions, frequency was used as a parameter.
The experimental procedure was as follows. Container A (transparent; inner dimensions: width 4.9 cm x depth 25.5 cm x height 17 cm) was placed on a non-slip sheet. Sand sieved to a grain size of #250–500 was added to a thickness of 1 cm, and water was added to a depth of 3 cm. The motor was operated for 5 minutes, and the upstream and downstream lengths of the formed WRs were measured. The motor side was defined as upstream. The experiment was recorded for 5 minutes while the motor was running. A 10-second segment from the recorded video was used to calculate frequency. Steps 1-4 were repeated while changing the motor output.
3. Results
By varying the motor output, clear ripple marks were formed at frequencies between 1.0 Hz and 2.8 Hz. Results obtained under nine different motor output conditions are shown in Fig. 2 and 3.
4. Discussion
The results demonstrate that model experiments of WRs can be conducted by varying frequency. All measured values fell within the RSI range of wave ripples, supporting the initial assumption.
However, the experimental setup had limitations. The narrow width of the tank restricted lateral flow, resulting in flow primarily in one direction and making it difficult to reproduce complex natural flows such as wind or river currents. Additionally, only a single type and grain size of sand was used, rather than mixed sediments. These factors present challenges in accurately reproducing WRs.
5. Future Work
It was observed that even at the same frequency, different motor outputs produced different ripple forms. Therefore, future work will involve more precise measurements and systematic recording of ripple characteristics. Furthermore, frequencies below 1.0 Hz and above 2.8 Hz, where clear ripples were not formed, will be tested using a container with greater depth to enable further quantification.
Since this study was conducted under specific conditions, it does not fully represent natural environments. Future experiments will vary parameters such as grain size and water depth to expand the range of experimental conditions.