TORSIONAL

VIBRATIONS

Torsional vibrations

• Torsional vibration is angular vibration of an object—commonly a shaft along its axis of rotation. Torsional vibration is often a concern in power transmission systems using rotating shafts or couplings where it can cause failures if not controlled.

The arrow shows where the sensor measures the torsional vibration .

Torsional Vibration Analysis (TVA)

• Torsional Failures: • Excessive torsional vibration and

resonance leads to very expensive failures such as damaged shafting, couplings, gears, auxiliary equipment, and more. Repair Machinery systems continue to increase in speed and horsepower leading to higher torsional excitation. Preventing failures caused by this requires adequate analysis over the equipment’s intended range of operating conditions.

APPLICATIONS OF TVA

• Reciprocating Gas Compressor• Screw Compressors • Plunger & Centrifugal • Flexible Disk vs. Torsionally Soft

Coupling • Optimum Flywheel Size • Crankshaft Detuners

Crankshaft torsional vibration

• Torsional vibration is a concern in the crankshafts of internal combustion engines because of several factors.

• Alternating torques are generated by the slider-crank mechanism of the crankshaft, connecting rod, and piston. – The motion of the piston mass and

connecting rod mass generate alternating torques often referred to as "inertia" torques

– The cylinder pressure due to combustion is not constant through the combustion cycle.

Measuring torsional vibration on physical systems

• The most common way to measure torsional vibration is the approach of using equidistant pulses over one shaft revolution. Dedicated shaft encoders as well as gear tooth pick up transducers (induction, hall-effect, variable reluctance, etc.) can generate these pulses. The resulting encoder pulse train is converted into either a digital rpm reading or a voltage proportional to the rpm.

REFRENCES

• www.wikipedia.com• general applications of torsional

vibrations by J . X CHANG