Mandar Phadnis

There is a pressing need to transition from fossil fuels to renewable energy, given the escalating impact of climate change. Wind energy offers a promising solution as a clean and sustainable alternative to reduce harmful emissions generated using oil and gas sources.

While the rapid growth of the wind energy sector underscores its potential, wind energy remains a vibrant area of research driven by the continual need to improve power production and drive down costs. By improving the technology and efficiency of wind energy, we can accelerate the necessary shift towards a greener future.

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The experimental test setup in the wind tunnel at the ForWind Center with the full-scale wind turbine and the active grid

My research as a PhD student at the University of Colorado Boulder (CU) focuses on developing control strategies for novel wind turbine systems to push the boundaries of current technologies in the field of wind energy. I have been primarily involved in developing controllers for extreme-scale wind turbines and floating offshore wind turbines. As part of my research, I was exploring a wind turbine control strategy, that can predict incoming gusts of wind to protect the wind turbine from excessive loading.

Reduced structural loading can reduce maintenance costs and extend the turbine lifespan. This strategy, initially proposed by Dr. Dan Zalkind, can also be used to boost power production during times of calmer wind. The ForWind Center for Wind Energy Research at the University of Oldenburg in Germany houses a state-of-the-art wind tunnel with an active grid capable of generating repeated realistic wind conditions.

It also houses a scaled wind turbine called Model Wind Turbine Oldenburg (MoWiTO), equipped with advanced actuation and sensing capabilities. This advanced wind research facility offered me an opportunity to test out our control strategy on a model wind turbine under realistic wind conditions inside the wind tunnel facility at the ForWind Center.

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The university library, where Mandar Phadnis liked to continue working after his work in the wind tunnels

My advisor at CU, Professor Lucy Pao, has had a long-standing and fruitful research collaboration with Professor Martin Kühn and Dr. Vlaho Petrović at the ForWind Center. Multiple researchers from our lab have visited ForWind to conduct research over the years. Professor Kühn invited me to visit Oldenburg and conduct experimental research in the wind tunnel at the ForWind Center.

Accordingly, I applied for a short-term research grant through the DAAD portal. The application process was straightforward and timely, and I was very grateful to receive a grant for a 4-month visit funded by DAAD-Stiftung, starting from mid-December 2023 to mid-April 2024. My PhD advisor from CU was in Delmenhorst for part of my visit, which allowed all of us to meet in person at ForWind and coordinate my research plan during the crucial initial weeks.

Through this research visit, I got an opportunity to work very closely with Professor Kühn and his wonderful team of researchers, present my work to their group, and understand the cutting-edge research being conducted at ForWind.

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View from the office on a warm winter morningg

The preparations for my visit to Germany began a few months in advance. Being a citizen of India and an international student in the US, I needed a German national visa to be able to stay for the duration of my visit. DAAD-Stiftung was very prudent and helpful in providing all the documents required for my visa interview, which took place at the German Consulate in Los Angeles.

The visa interview turned out to be a very positive experience, especially since I was being funded by DAAD-Stiftung, and I received my visa within a couple of weeks. I started looking for apartments in Oldenburg while in the US, but I soon realized this was more complex than I had anticipated. My advisor reached out to the staff at ForWind, and I was happy to be put in touch with the manager of a guesthouse right on campus at the University of Oldenburg.

I was offered an apartment at the guesthouse starting January 2024 for the remainder of my visit. I jumped at this opportunity and signed the contract. This meant I only had to arrange accommodation for part of December.

Lucy Pao

Group photo with the ForWind team of researchers at the Oldenburg Christmas Market

I arrived in Oldenburg on December 10th and rented an Airbnb in Oldenburg for a week. It was a pleasant 30-minute walk from ForWind. Being from Colorado, the mild German winter was a welcome change, and I enjoyed walking to work, although there were multiple buses available. On my first day at ForWind, I was welcomed by my hosts, Professor Kühn and Vlaho.

Vlaho assigned me an office on the same floor as their research group. The office has two large desks and a huge window. My advisor was also visiting ForWind, and she introduced me to many of the researchers across the three floors of the research building.

I was also given a tour of the facility and a peek into the wind tunnel, where I would eventually conduct my research experiment. I spent the first week getting to know the people, attending research group meetings and presentations, and going to group lunches at the university canteen (Mensa) to enjoy authentic German cuisine.

The group lunches were a great way to get to know other researchers working at ForWind, understand their work, make deeper connections, and get tips from them to make my stay even better. I felt very warmly welcomed and included in the group, and it was a breeze to fit in and participate in their conversations and activities, despite the language barrier.

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The favorite café, the daily used bus stop and a picture of Mandar Phadnis at the Oldenburg Christmas market

Since December is a festive month in Germany, many people recommended that I travel around the country and experience the Christmas markets. My girlfriend decided to join me for Christmas and New Year. We spent the first few days staying in a hotel at the Bremen Hauptbahnhof. I traveled for work to Oldenburg every day, which was a convenient, 1-hour train ride that was also economical using the Deutschland Pass.

During this time, we explored the wonderful Christmas markets at Oldenburg, Bremen, and Hamburg, enjoying warm Glühwein with brötchen in the cold weather. We visited parks, cathedrals, town centers, and shopping malls. We were pleasantly surprised by the amount of people outside celebrating, the decorations, the size and scale of the Christmas markets, and the festive spirit.

We also rented a car to visit Berlin for a few days, exploring the rich culture and history and enjoying international cuisines. We concluded our vacation in the Netherlands, visiting Delft, Rotterdam, and Den Hague and spending New Year’s Eve in Amsterdam, enjoying the fireworks around the city.

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Mandar Phadnis and his girlfriend on a voyage of discovery in Germany and the Netherlands

After traveling, it was time to ramp up my research. I started by using a simulation model of the scaled wind turbine (MoWiTO) from the wind tunnel to implement and tune the controller I intended to test during the experiment. I used Matlab/Simulink software by Mathworks to code the controller and integrate it with the simulation model implemented in OpenFAST.

I used data from previous wind tunnel experiments to resolve discrepancies between the simulation model and the wind turbine to reduce the chances of unexpected behavior during the experimental phase. The hardware in the wind tunnel did not work with the Matlab/Simulink, which I generally used to run simulations, but instead worked with a software called LabView developed by National Instruments. So, the next step was to convert the final control design from Matlab/Simulink into LabView.

Now, LabView has a steep learning curve, but with the excellent mentorship I received from Vlaho, who is the in-house LabView expert at ForWind, and a lot of hours spent reading documentation and tutorials, I was able to get the controller working in LabView I worked with Vlaho to describe the gusty wind sequence I needed in the wind tunnel to test out the controller in the tunnel, which the turbulence experts at ForWind were able to provide, and I was finally prepared for the tunnel experiment.

The wind tunnel needs to be reserved for experimental testing. I was assigned a week in the wind tunnel to perform my experiment. Testing in the wind tunnel was the most exciting week I had during my time at ForWind. We spent long, grueling hours, sometimes going close to midnight, getting our setup working with the placement of the wind turbine, calibration of the sensors, and testing of the hardware. It was my first experience working with wind turbine and tunnel hardware and I learned a lot about the difficulties and complexities of executing a realistic scenario within a lab setting.

After a lot of trials, debugging, and hardware troubleshooting, we were able to run the experiments successfully. The results from the tunnel experiment validate the control strategy that may be applied to commercial wind turbines to improve power capture without risking an overspeed shutdown. It was one of the most rewarding experiences of my visit.

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The last day in the pension apartment. With his luggage packed on his very last day in Germany after, as he said himself, four months full of wonderful memories!

After the experiment was complete, I also got the opportunity to visit wind energy research groups at nearby universities and attend a control systems conference to present my research. In particular, I visited TU Delft in the Netherlands and met with wind energy researchers for one-on-one meetings and a tour of their lab facilities. Following this, I attended the Benelux Meeting on Systems and Control in Blankenberge, Belgium, to present my research to a European audience.

Outside of work, I spent time at the gym, taking long bike rides to neighboring towns, and going on morning runs during the weekends. My colleagues at ForWind frequently invited me to join them for indoor bouldering, an activity I had barely tried before. Initially hesitant, I quickly discovered how much I enjoyed it and have continued to pursue it regularly, even after returning to the US.

The challenge of bouldering has given me a new hobby, and I'm grateful to my colleagues for introducing me to it. They also invited me to frequent group dinners at all the best restaurants around Oldenburg and Bremen and to join them on Kohlfahrt, a local customary cabbage tour.

This way, I had a chance to experience the full diversity of cuisines Germany had to offer. While I could not pick up much of the German language outside of basic phrases, since returning to the US, I have prepared Grünkohl and Glühwein myself for dinner on more than one occasion. I will value the memories and connections I made over this visit for many years to come.

Overall, my four-month research visit was an enriching and transformative experience. I would like to thank my hosts, Professor Martin Kühn and Dr. Vlaho Petrović at the ForWind Center for Wind Energy Research, and my advisor, Professor Lucy Pao, for making this stay possible. I am deeply grateful to the KSB Stiftung for their generous funding, which was critical for this research visit.

It allowed me to experience a different culture with a rich history and way of life. I would like to thank all the staff at DAAD-Stiftung, especially Stefanie Lohmann, for her help and advice throughout this process, which made my visit a great success.