BISOPE series 88 Natural frequency of solids in fluid flow

BISOPE series 88- Natural frequency of solids in fluid flow ((Method of calculating natural frequency of horizontally crossing tubes or pipes in wind, water, or steam)---------------------------------------------------------------------------------------

There is self-excited vibration caused by friction between solids and fluids.

It refers to vibration that is self-excited, but its true meaning is caused by the fluid force of the fluid (flow induced).

This self-excited vibration is a type of nonlinear vibration that is difficult to predict and has various causes and results.

The fundamental cause is that dynamic loads (mass and velocity) exist in fluids.

 

For example, a placard or electric wire (galloping) shaking in the wind, an airplane wing (flutter), a propeller or oar shaking in water, a tube or valve that vibrates strongly when it reaches a singular velocity in heat exchanger steam are all included.

 

If you look closely, you can see that it is related to a certain unique frequency.

 

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Key! Natural frequency, fluid vibration, Karman vortex, pipe vibration

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BISOPE series 67 Comparison Solid sound and airborne sound

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BISOPE series 45- A Collection of Vibration Causes of Fluid Machines

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In rotating machines, vibration occurs due to centrifugal force due to mass imbalance and friction and impact between solids, but there is another source of vibration. It is self-excited vibration caused by friction between a solid and a fluid. This self-excited vibration is a type of nonlinear vibration that is difficult to predict and is accompanied by various causes and results. The root cause is that dynamic loads (mass and velocity) also exist in the fluid.

Representative fluid machines have a fan and a pump, and are classified according to whether the transported fluid is gas or liquid. Blower (more than 0.1kg/m²) and Compressor (more than 1kg/m²) are also called names.

Types of Fluid Vibration

 

Fluid vibration occurs in various ways, such as when the fluid is caused by an ideal balance of pressure, when irregular vibration is induced by the occurrence of turbulence, or when it is generated on the rear surface by friction with a solid.

The vibration time waveform shows irregularity, and the form of the spectrum has various expressions, such as when floor noise is large, when a frequency group is formed over a certain period (wide band), or when it appears as narrow-band discrete frequencies. The following table summarizes various phenomena of fluid vibration.

 

 

type of vibration

Causes and Symptoms