7 Types of Vibration: There Must Be Something You Don’t Know

Types Of Vibration

1. Resonance

When the system is forced to vibrate by external excitation, if the frequency of external excitation is close to the system frequency, the amplitude of forced vibration may reach a very large value. This phenomenon is called resonance.

A system has countless natural frequencies. We often study the system frequencies in a low range.

Resonance is a very high frequency term in physics.

Resonance is defined as the phenomenon that two objects with the same vibration frequency cause the vibration of another object when one vibrates.

Resonance is also called “resonance” in mechanics.

It refers to the phenomenon that an object makes sound due to resonance.

For example, when two tuning forks with the same frequency are close, one of them will make sound when vibrating, and the other will also make sound.

2. Vortex vibration

Vortex vibration refers to the vibration caused by the vortex shedding alternately after the flow around the solid web section under the action of mean wind.

The study of bridge vortex vibration is a branch of aerodynamics.

Vortex induced vibration of bridge is a kind of finite amplitude vibration with both self-excited vibration and forced vibration characteristics.

It can keep the vortex induced frequency unchanged in a considerable wind speed range, resulting in a “lock-on” phenomenon.

The finite amplitude calculation of bridge vortex induced resonance is a very important but extremely difficult problem.

At present, a relatively complete set of bridge vortex vibration analysis theory has not been formed at home and abroad.

In practice, a semi theoretical and semi experimental method is used to approximately estimate the amplitude of vortex induced resonance.

3. Flutter

Flutter refers to a self-excited vibration phenomenon under the action of aerodynamic force due to the elasticity and inertia of the structure itself and the coupling between flow and structure.

Buffeting usually refers to the forced response of the structure caused by the periodic aerodynamic force loaded on the elastic structure due to the unsteady characteristics such as flow separation and shock boundary layer interference.

In other words, under the traditional definition, classical flutter is a kind of self-excited vibration.

In addition, there is stall flutter at high angles of attack.

Some scholars believe that this kind of structural vibration with strong separation conditions coexists with flutter and buffeting.

4. Buffeting

Buffeting in aircraft refers to the vibration of aircraft components according to the natural frequency of the structure under the excitation of separated air flow or wake.

The main example of buffeting is the tail wing buffeting of an aircraft.

When the tail is in the wake of the wing, wing fuselage joint or other components, the disturbance in the wake forces the tail to vibrate strongly.

When an aircraft flies at a high angle of attack, it is particularly prone to tail flutter, which has caused serious accidents in history.

The buffeting of the wing comes from the separation of its own air flow.

In the transonic range, the boundary layer separation induced by shock wave is another important reason for the buffeting.

Buffeting limits the available lift coefficient and Mach number of the aircraft.

The measures to prevent buffeting are usually to rectify the aerodynamic shape and properly arrange the relative position between the tail and the wing and fuselage.

Buffeting is a random vibration, but it is regular in the frequency domain.

The main peak of its power spectrum generally corresponds to the first natural frequency.

Compared with flutter, although buffeting will not immediately damage the structure of the aircraft, the increased structural stress will reduce the fatigue life of the aircraft.

At the same time, buffeting will also have an adverse impact on the aerodynamic performance of aircraft, weapon system, mechanical and electronic instruments and equipment, as well as the comfort of passengers.

Severe buffeting may also cause the pilot to lose control ability, thus endangering the safety of the flight and the pilot.

Therefore, buffeting is considered as an important factor in aircraft design.

5. Surge

Surge is a kind of abnormal vibration of turbine compressor (also known as vane compressor) when the flow decreases to a certain extent.

Centrifugal compressor is a form of turbine compressor. Surge is very harmful to centrifugal compressor.

The generation of surge is related to the characteristics of fluid machinery and pipeline.

The larger the capacity of pipeline system, the stronger the surge and the lower the frequency.

The surge of fluid machinery will destroy the flow regularity of medium inside the machine, produce mechanical noise, cause strong vibration of working parts, and accelerate the damage of bearings and seals.

Once surge causes resonance of pipeline, machine and its foundation, it will also cause serious consequences.

6. Galloping

Galloping generally occurs in square, rectangular, rectangular and other structures with complex and irregular non streamline sections.

The mechanism of galloping is that the lift curve has a negative slope, which makes the air lift have a negative damping effect, and the structure can continuously absorb energy from the outside, thus forming a divergent vibration phenomenon similar to flutter.

According to the different generation mechanism, galloping can be divided into wake galloping and cross flow galloping.

Wake galloping is an unstable vibration caused by the downstream structure excited by the flow bypassing the fluctuation of the front structure.

For example, the cables of cable-stayed bridges and suspenders of suspension bridges are most prone to wake galloping.

Cross flow galloping is a divergent bending self-excited vibration caused by the negative slope of the lift curve.

This negative slope makes the displacement of the structure consistent with the direction of air force in the process of vibration, and the structure continuously absorbs energy from the outside, resulting in unstable vibration.

Cross flow galloping generally occurs in flexible lightweight structures with angular non streamline sections.

Cables and suspenders in suspension system bridge structures are most likely to occur cross flow galloping.

In addition, there is the possibility of galloping divergence for girder steel bridges with small width height ratio, high and flexible long-span cable-stayed bridges, suspension bridge towers and main beams of continuous steel frame bridges in the maximum cantilever construction stage.

7. Vortex street

Vortex street is an important phenomenon in fluid mechanics, which is often encountered in nature.

When the steady incoming flow bypasses some objects under certain conditions, the two sides of the object will periodically fall off the double row line vortices with opposite rotation direction and regular arrangement.

After nonlinear action, Carmen vortex street is formed.

If the water flows through the pier and the wind blows through the tower, chimney and electric wire, Carmen vortex street will be formed. Because the vortex street was proposed by Carmen, it is also called Carmen vortex street.

Chinese mechanics benchmarking figures Qian Xuesen, Guo yonghuai and Qian Weichang have all worked in Carmen laboratory.

If the alternating shedding frequency of vortex street coincides with the acoustic standing wave frequency of the object, resonance will also occur.

Industrial preheaters and boilers are mostly composed of circular tubes. When the fluid flows around the circular tube, the alternating shedding of Carmen vortex street will cause the vibration of the gas column in the preheater box.

If the alternating shedding frequency of vortex street coincides with the acoustic standing wave frequency of the object, it will cause acoustic resonance and make the tube box vibrate violently. In serious cases, the vibration drum of the preheater tube box will be staggered or even broken.

If the natural frequencies of the pipe box and gas are changed to stagger them from the shedding frequency of the Carmen vortex street to avoid resonance, the damage of the equipment can be prevented.

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