He's just trying to get the necessary information about your project to help you. If you bring your car to a mechanic and all you say is "my car is doesn't work" they can't help you. Plus this is also a forum so it's like doing the same thing over the phone which makes it even more impossible. We are not mind readers.
I've always wondered if resonant frequency could be used to measure fuel level. Anyone tried?
Colleagues who help you solve problems using a hammer are the most valuable.Interesting idea, especially of a tank on a tower. The mass in the tank will change the natural frequency of the system. Probably going to be far from a linear relationship as there would be many factors involved.
If the tank was outdoors, the wind could excite the natural frequency or some kind of "thumper" could be used.
[Mandatory story] My group in a naval shipyard performed machinery condition / vibration analysis on rotating machinery (including some of that types of machines Ron was responsible for). When we had concerns about natural frequencies being close to a forcing frequency of a machine, we'd break out our 16 pound no-bounce (shot-filled) sledge hammer. A bump test on the machine will excite its natural frequencies. No lumberjack swings at the machine but just a gentle thud to make it vibrate.
One day the chief design engineer followed us out to a ship when we had to do a bump test. The machinist general foreman had called him, complaining we were beating on his machines with a sledge hammer, and he wanted to see for himself. We set up the tape recorder and accelerometers and hit the machine with out sledge hammer... with about a 4 inch swing. Thud.
"That's it? That's all you do?!?" the chief design engineer asked. Yep, not very exciting, is it?