Solution methodology of vibration & control

• Vibration is a mechanical phenomenon periodic back-and-forth motion of the particles of an elastic body or medium.

• 

• There are three different types of vibration, which are:

Free or Natural Vibration.

Forced Vibration. 

Damped Vibration.

• Vibration can be desirable: for example, the motion of a tuning fork, the reed in a woodwind instrument or harmonica, a mobile phone, or the cone of a loudspeaker.

Condition Monitoring using vibration analysis :

- Continuous monitoring of your assets helps you detect signs of premature or abnormal wear. Such situations could result from any number of issues, such as gear faults, lubrication problems, misalignment, imbalances, or defective components. Conditions are monitored in real-time, giving you an accurate snapshot of your systems’ health at any given moment. 

- Troubleshooting becomes easier and more efficient, as well. With access to machine-level vibrational data over time, specific anomalies become easier to pinpoint, reducing human-hours spent on diagnosing problems and reducing unnecessary service calls.

- Gearbox diagnosis:

Fig.1 Time Domain Signal

Fig.2 Frequency Domain Signal

- Vibration monitoring is one of the most effective ways to detect and prevent equipment failure or downtime. It can screen most faults including imbalance, misalignment, looseness, and late-stage bearing wear, providing precipitous warning of impending failure.

- The "Fast Fourier Transform" (FFT) is an important measurement method in the science of audio and acoustics measurement. It converts a signal into individual spectral components and thereby provides frequency information about the signal.

Fig.3 FFT

Damping control in semi-active car suspension :

• This system was first introduced in 1954 by Citrozen.

• semi-active suspension is a type of automotive suspension systems that controls the damping force of the stock absorber in response to input from the continuosly varying road surfaces.

Particle Damping method and its application

• What is Particle Damping?

Particle damping is to increase damping performance in current technology. Particles are attached to the vibrating structure. The particles take up kinetic energy of the element and convert it into heat energy with the help of collisions between the particles and the element wall. Energy dissipation occurs in the particle damping method due to inelastic and frictional loss collision between particles. Selection of particle damping material having high damping to achieve by converting kinetic energy of the element to heat

Particle impact damping offers the potential for the design of a better passive damping technique. Passive damping has minimal impact on the strength, stiffness and weight of a vibrating element. With a proper choice of particle material, this technique appears to be independent of temperature and is very durable. Mainly two types of simulation done on particle damping. (a) DEM (Discrete element method) (b) Finite element method. 

• Particle Characteristics:

The working principle of particle technology is simple. Different types of ball

material are placed inside the cavity. Cavities are partially and wholly filled.

Depending upon the size of the hole, particle size is less than 0.2. So a single

hole contains numbers of particles in the order of 100-500. Selection of high

density particles are performed effectively to reduce the vibration. Packing ratio is

the major factor of particle damping method. 

Volumetric Packing Ratio: 

The particles can be filled either fully or partially in the containing holes.

Packing ratio is the ratio of volume of filled space to the unfilled volume in the

containing holes. A packing ratio of 1 renders the maximum damping effect. 

Active control of vibrations in Helicopters by periodic optical method -

- A considerable effort has been devoted to the development of active control

systems for the attenuation of vibrations in helicopters. Besides improving the

comfort of the crew and passengers, such an attenuation would be profitable to

reduce fatigue in the rotor and structure of the aircraft and to protect from damage

on-board equipment.

- Various approaches to this problem have been proposed in the literature; in

particular, three main lies of thought can be identified:

•  Control of the vibratory response of the airframe, by acting on the airframe. 

•  Control of the vibratory response of the airframe by acting on the main

rotor.

•  Rotor control by measurement of the vibratory accelerations/loads on each

rotor blade individually.

In an IBC framework, the control input is the pitch angle of each blade of the

main rotor, while one tipically consider as output acceleration measurements

taken at various locations on each blade, or the measurements of the vibratory

loads each blade transmits to the rotor hub.

One should observe that the dynamics of a rotor blade can be satisfactorily described by a (linear)

time-invariant model only in the case of a hovering rotor, while in forward flight

such dynamics turns out to be time-periodic, with period equal to the rotor

revolution period. Of course, the model is also a function of the velocity of the

aircraft.

Stages of the Study:

• Precise formulation of the disturbance rejection problem.This formulation

calls for the definition of an “input equivalent disturbance” (IED).

•  Development of the control design technique.

• The control strategy is then applied to the problem of attenuating helicopter

• vibrations. 

The determination of the IED can be performed according to two different rationales: in both approaches, the main idea is to estimate the disturbance characteristics from input-output data by means of a Kalman filter. The first rationale (direct method) is based on the estimation of the IED directly, whereas the second one (indirect method) consists in estimating the output disturbance and then “translating” it to the input.

References -

1. P Raghava Madhyastha, Ramesh Kurbet, Ajit Prasad S.L“Detection of Gear Teeth Damage through Sound and Vibration Signal Analysis of Austempered Ductile Iron Gear”,August 2020.

2. Machinery Fault Diagnosis | Condition monitoring of Machineries | Case studies | Vibration Analysis

Blog by students of,

Vishwakarma Institute of Technology, Pune

Third-Year Mechanical Department

Division D, Batch 1, Group 1

For DOM Home Assignment

Akash Salunkhe (3)

Mandar Salvi (4)

Ganesh Sarak (11)

Yashodhan Shendge (15)

Dhiraj Solunke (22)