Are you confronted with a structural dynamics problem?
Three elements are characterizing a structural dynamics problem (Fig. 1):
Basically: If we know two of the three we can determine the third.
|Fig. 1: The three elements of a structural dynamic’s problem.|
The most simple structural dynamic’s problems are those, where the system Response Y is measured only and where this response can be rated using standards. However, such standards do not always exist and they tend to being quite vague in Switzerland and Germany. As a consequence, the test engineer has to take responsibility based on experience (Project Stallikon).
Experimental Modal Analysis
The standard structural dynamic’s problem when it came to civil engineering applications decades ago: Determination of the Transfer Function H through measurement of the Excitation X and the Response Y (Forced Vibration Testing, FVT) has mainly been replaced through Ambient Vibration Testing, AVT,in the last ten years. With AVT, the system dynamic characteristics are determined through processing Response signals Y only. Both procedures, FVT as well as AVT, are also called Experimental Modal Analysis.
Vibration Measurements with Determining Excitation, Transfer Function and Response
The most beautiful problems are those, where all three elements Excitation X, Transfer Function H und Response Y can be determined experimentally. Firstly, the Transfer Function H is determined from an Experimental Modal Analysis, and secondly, an operational state of the structure (e.g. moving loads) is investigated into experimentally with measuring X and Y. As a consequence, the possible structural dynamics problem related to the Response Y (e.g. under the passage of moving loads) can be solved through working either on the Excitation X or on the Transfer Function H. Everything is under control! But the effort can be very important (PhD. Diss. Cantieni).
The most difficult structural dynamic’s problems are those where some ideas exist concerning the properties of X und H and the engineer is asked to present a prognosis concerning the system Response Y. Success is quite rare in such cases (Project Langensand).
Structural dynamics‘ problems are never boring!
Structural dynamics‘ problems have been our daily business for more than 40 years.