Wind blowing over the ocean surface energizes water waves on the surface and induces currents and turbulence in the water. This wind-water interaction regulates the transfer of gases, energy, and momentum between the atmosphere and the ocean, making it a critical component of Earth's climate system. ETH's new wind-water-wave tunnel has been constructed to enable experiments on the interaction between airflow and water flow. Among other capabilities, a fan circulates air over the water surface at speeds between approximately 3 and 20 m/s, causing surface waves to grow over the course of the tank length.
The first studies being carried out in this facility are probing the characteristics of the turbulence generated just beneath the surface by the wind.
The student will employ Fourier transform profilometry to measure the characteristics of the waves produced by the wind over a range of conditions. This experimental method involves projecting a pattern onto the surface of the wavy water and, using a high-speed camera, recording images of the pattern as viewed from above. The apparent modulation to the pattern in the images caused by the surface's waviness is then used to computationally infer the local surface elevation.
Processing of the images will thus reveal time-resolved measurements of the local surface elevation over some spatial area. This elevation field will primarily consist of waves propagating in the wind-ward direction, but will also involve transverse movements. Understanding the three-dimensional nature of the wave field is critical to our interpretation of separate water velocimetry measurements, which in some cases resolve the flow and surface position in only a single plane. More fundamentally, the results will be used to understand the initial stages of wind-wave growth (in which the wind has only had enough time to produce disorganized ripples) and the waves' roles in generating three-dimensional turbulence in the water just beneath the surface.
Wind blowing over the ocean surface energizes water waves on the surface and induces currents and turbulence in the water. This wind-water interaction regulates the transfer of gases, energy, and momentum between the atmosphere and the ocean, making it a critical component of Earth's climate system. ETH's new wind-water-wave tunnel has been constructed to enable experiments on the interaction between airflow and water flow. Among other capabilities, a fan circulates air over the water surface at speeds between approximately 3 and 20 m/s, causing surface waves to grow over the course of the tank length.
The first studies being carried out in this facility are probing the characteristics of the turbulence generated just beneath the surface by the wind.
The student will employ Fourier transform profilometry to measure the characteristics of the waves produced by the wind over a range of conditions. This experimental method involves projecting a pattern onto the surface of the wavy water and, using a high-speed camera, recording images of the pattern as viewed from above. The apparent modulation to the pattern in the images caused by the surface's waviness is then used to computationally infer the local surface elevation.
Processing of the images will thus reveal time-resolved measurements of the local surface elevation over some spatial area. This elevation field will primarily consist of waves propagating in the wind-ward direction, but will also involve transverse movements. Understanding the three-dimensional nature of the wave field is critical to our interpretation of separate water velocimetry measurements, which in some cases resolve the flow and surface position in only a single plane. More fundamentally, the results will be used to understand the initial stages of wind-wave growth (in which the wind has only had enough time to produce disorganized ripples) and the waves' roles in generating three-dimensional turbulence in the water just beneath the surface.
The project will involve the following steps:
- Consulting literature to understand (a) the current understanding of the physics of wind-driven wave growth and (b) the implementation of Fourier transform profilometry;
- Selecting appropriate materials (projector, water dye, etc) for the project;
- Developing a small-scale version of the projection and imaging system in a water tank (at ETH Zentrum) and writing Python code to process the data;
- After initial testing, moving the system to the larger wind-water-wave tunnel at Empa in Dübendorf and acquiring data there under a range of wind speeds;
- Using the measured results and existing literature to better understand the development of wind-driven surface waves.
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The project will involve the following steps:
- Consulting literature to understand (a) the current understanding of the physics of wind-driven wave growth and (b) the implementation of Fourier transform profilometry; - Selecting appropriate materials (projector, water dye, etc) for the project; - Developing a small-scale version of the projection and imaging system in a water tank (at ETH Zentrum) and writing Python code to process the data; - After initial testing, moving the system to the larger wind-water-wave tunnel at Empa in Dübendorf and acquiring data there under a range of wind speeds; - Using the measured results and existing literature to better understand the development of wind-driven surface waves. \end{itemize}
The project is especially well-suited for students with interests in experiment design, data analysis, and fluid mechanics. Interested students should apply with their their CV, full transcript, and if applicable, bachelor's thesis and semester project, submitted via SiROP or to daruth@ethz.ch.
The project is especially well-suited for students with interests in experiment design, data analysis, and fluid mechanics. Interested students should apply with their their CV, full transcript, and if applicable, bachelor's thesis and semester project, submitted via SiROP or to daruth@ethz.ch.