How can resonance be avoided

Different sources of vibration behave differently with changing speed. For instance, unbalance typically causes vibration amplitudes that increases exponentially with increasing speed. Misalignment typically causes vibration that increases linearly with increasing speed. Resonance however, is characterized by a large increase in vibration at the resonant frequency but generally lower amplitudes at all other speeds.

The cascade plot below shows an example of typical vibration exhibited during startup of a machine with a structural natural frequency in its operating speed range. Often known as an impact test or a modal analysis, this is a method that allows us to experimentally determine the natural frequencies, mode shapes, and damping of a test structure. If any one of the calculated natural frequencies are within or near the operating speed range of a machine, there is the potential for a resonant condition to occur.

Typically field modal testing is performed with a calibrated modal impact hammer. The hammer contains a load cell in the tip which provides a direct measurement of the impact force of applied to the system.

A spectrum of this ringdown can be used to determine the natural frequencies of the system. This test is typically performed with the machine turned off, however advanced signal processing can also be used to average out running condition vibration and identify only the free vibration. Resonance occurs when the amplitude of an object's oscillations are increased by the matching vibrations of another object.

How do you use resonance in a sentence? The resonance in the singer's deep voice made the song sound more powerful. The effects of resonance were studied by the music students. The two piano keys played together provided a good example of resonance.

What is resonance sound? This is known as resonance - when one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion.

The word resonance comes from Latin and means to "resound" - to sound out together with a loud sound. Why is resonance useful? One use for resonance is to establish a condition of stable frequency in circuits designed to produce AC signals. Just as a pendulum can be used to stabilize the frequency of a clock mechanism's oscillations, so can a tank circuit be used to stabilize the electrical frequency of an AC oscillator circuit.

What are the advantages of resonance? A whole lot of applications depend on resonance. All transmission and receiver business depends on resonance. It is possible to get very high voltages with small voltage using near resonance values of L and C. When should resonance be avoided? Already a Member? Join your peers on the Internet's largest technical engineering professional community.

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Hi all, I would like to know what would be your design sequence for structures which are vulnerable to resonance. This resonance issue occurs especially when you have light weight structure where cycling loads wind, earthquake, etcc Theoretically, each structure has natural vibaration modes and if any loads comes with in range of that modes same vibration frequencies this will amplify the effect of applied load and inevitably will result in collapse.

But how we are supposed to calculate how much time that structure will sustain to the applied load when it has the resonance? Your comments will be appreciated?

I don't think collapse is inevitable; but if you design something with a natural frequency that is similar to the frequency of whatever the use is, then you will have usability issues. How to avoid it? In practical terms excitation should generally be broadband if your trying to excite a structure with the objective of finding a particular or all resonances. There will be a relationship between the excitation and the first mode, but to find that one would perform some practical test or mathematically model the system, for example in a simulation.

We would recommend practical test to find a mode rather than a mathematical process as structures more complex than a simple beam tend to be rather difficult in terms of finding boundary conditions and free states. My question is, why is it absolutely necessary to use impact hammer, rather frequency response function to determine the natural frequency of the system?

If use accelerometer and excite the object by any means , lets say by wood or something, it should be regarded as a natural frequency. Pingback: Vaibhav — lester If you have a structure like a bridge for example, it will have a natural frequency.

The engineers who design the bridge, will calculate what this should be from their design, the good engineers will validate this guess once the bridge is constructed.

In any case the bridge will have a natural frequency. The affect of wind, will again cause excitation of the bridge. The engineers will have designed the bridge in such a way that the natural frequency and the frequency excited by t he wind will be different.

Can I fix it bolting on heavier blocks or better yet drilling holes in it or milling channels into its surface? The long answer is more complex, to change the natural frequencies you have to change the mass or the stiffness of the structure. You can change the mass by adding the heavy blocks you mention, or by changing the structure itself, milling or drilling, but the milling or drilling will also change the stiffness.

So I recommend adding additional mass, then the stricture is unchanged and you can always go back to your current configuration. It really depends on the testing your doing however, if you change the behaviour of the bracket, you are in effect changing the behaviour of the vibration table.

So please think about it like this, are the natural frequencies of the bracket, frequencies of interest to the test? If so additional thought maybe required, for example you would have to consider where you measure the input force to the structure.

You could also consider some form of damping to the bracket, something that could absorb a lot of the energy that is creating the noise. Perhaps a very tough rubber mount for example, this is in effect changing the stiffness. But again the force and frequency that the test piece is then subject to has to be considered. Perhaps you could suggest the frequencies of interest for your test?

Are they outside the natural frequencies you have mentioned? But after adding it, my mode shapes are completely change into a new deformations in each modes.

Is that valid? Second question is how much percentage should i shift natural frequencies? We understand your objective, please understand if you have a simple structure and then redesign the structure, the mode shapes will most likely change. It would appear you have significantly changed the structure, therefore one would expect a significant change to the mode shapes. If you are unsure, perhaps you could check the equipment you use to capture and analyse the mode shapes.

Regarding your second question, only you can answer. The natural frequency should be outside the range of frequencies normally excited by the standard operation of the equipment. It depends on the operating conditions of the equipment and the natural frequency.