Vibration analysis becomes a concern of mechanical system and engineering. Vibration analysis is performed to test some equipment and find whether there are problems within it. When a problem is found, it is mush easier to decide further treatment to fix it that the equipment can work well the way it used to be.
Vibration analysis includes two types of vibration, free and forced vibration. Free vibration happens when a mechanical system is set off with an initial input and then allowed to vibrate freely. On the other hand, forced vibration is when an alternating force or motion is applied to a mechanical system, like those happen in a shaking washing machine due to an imbalance. Hence, we only talk over free vibration.
Vibration testing becomes a part of the process in vibration analysis which includes the use of electrohydraulic shakers (low frequencies) and electrodynamic shakers (high frequencies). There are two types of vibration testing, random and sine test. Sine test is done to check the structural response of the device under test (DUT) while the random one is performed to more closely replicate a real world environment, such as road inputs to a moving automobile.
If you want to understand the basics of vibration analysis, simply learn about the simple mass–spring–damper model. This model is an example of a simple harmonic oscillator, even for complex structures of a machine or engine. In case you want explore focus on the concepts in vibration analysis, you can go on the next paragraphs.
Within vibration analysis, you will find what we call as free vibration without damping. On the mass–spring–model, the force applied to the mass by the spring is proportional to the amount of the spring. The proportionality constant is the stiffness of the spring and has units of force/distance. The negative sign shows that the force is always opposing the motion of the mass attached to it, just like what is said in Newton’s law of motion (the second).
The sum of the forces on the mass then generates ordinary differential equation. In case we start the system to vibrate by stretching the spring by the distance of A and letting go, the solution to the above equation says that it will oscillate with simple harmonic motion that has an amplitude of A and a frequency of (fn). The number (fn) is one of the most important quantities in vibration analysis and is called the undamped natural frequency.
Should you know about the mass and stiffness of the mechanical system in vibration analysis, you can determine the frequency at which the system will vibrate once it is set in motion by an initial disturbance. Every vibrating system has one or more natural frequencies that it will vibrate at once it is disturbed.
Then, in vibration analysis, you can understand vibrational motion with conservation of energy point of view. Take the example of mass-spring model. Once you let go of the spring, it will return to its un-stretched state (which is the minimum potential energy state). At the point where the spring has reached its un-stretched state all the potential energy that you provided by stretching it has been transformed into kinetic energy.
On the other hand, free vibration with damping in vibration analysis means that you need a “viscous” damper to the model that outputs a force that is proportional to the velocity of the mass. The damping is called viscous because it models the effects of an object within a fluid.
The most interesting point in vibration analysis is called as underdamping. This could happen when the damping is small enough that the system will still vibrate, but eventually, over time, will stop vibrating. Then, you will also find the terms of damping ratio. It is just a ratio of the actual damping over the amount of damping required to reach critical damping.
Damped and undamped natural frequencies are also the concern of vibration analysis. The damped natural frequency is less than the undamped natural frequency, but for many practical cases the damping ratio is relatively small and hence the difference is not significant.
Thus, we think it is enough, discussing the concept of vibrational analysis. To get more accurate measurement, you need special tool, which is called as vibration analysis meter. Besides, this tool will be in good performance if you equip it with vibration analysis accessories, like microphones for vibration analysis. Also you need advanced vibration analysis software for easier measurement. Those instruments will be a complete solution to fix machinery problem.
