Sound is produced by oscillatory motion due to the vibrations in machines and structures. Sound waves are therefore composed of the oscillatory motion of the fluid (typically air or water) molecules. The simplest type of oscillation in vibration and sound phenomena is the simple harmonic motion, which is nothing but a sinusoidal wave.
The analysis of noise and vibration is a very important aspect of product development. Excessive noise can cause hearing impairment, discomfort, stress and possibly trauma. Vibration too can cause discomfort, injuries and disease in humans. Not only is noise and vibration harmful to humans; it also affects the machine or the structure adversely. A few examples of machines where noise and vibration analysis is needed are vehicular engines, pumps, compressors, etc. The automobile industry especially needs their motor cars to run as smoothly as possible. However, vibration analysis is also needed in other engineering verticals. If vibration control is unsuccessful, it will cause fatigue in the machine or the structure, ultimately resulting in its failure.
In some cases, the vibration and noise need to be curbed to comply with statutory requirements. An example of such a requirement is the power generator.
In order to identify the sources of vibrations and noise, extensive analysis of measured signals from different tests is often necessary. A lot of advanced equipment and software (like OptiStruct from Altair) is often used to investigate noise and vibration signals in laboratory and in-field environments. Noise and vibration analysis needs a multidisciplinary approach and a good understanding of mechanics, electronic measurement techniques, sensor technology and signal analysis.
Noise and Vibration Analysis Software
In the 1980s, vibration and noise testing was solely a field or laboratory job, where actual machines/structures were tested for fatigue. The introduction of improved processing power has now ushered in a new generation of predictive software that makes analysis possible without having to develop a product first. Analysis of vibrations is most commonly done using finite element analysis (FEA), through normal mode analysis, etc. Finite element analysis is a technique that is very important in modelling the response of structures to dynamic loads. In essence, FEA is a numerical technique in which a continuous elastic structure, or continuum, is divided (discretized) into small but finite substructures, known as elements. Elements are interconnected at the node and can be manipulated using the software. Often, FE modelling begins with the import of CAD geometry into a FEM preprocessor and with the meshing of the geometry. Normally a 3D CAD geometry is available, which you can mesh with tetra elements.
Noise and Vibration Analysis Services(NVH)
As seen above, noise and vibration analysis is a highly challenging field that involves multiple domains. Just like Kinematics and Multibody Dynamics, no single software can suffice to serve all the demands of analysis. Why is testing by software a better option than field testing? For one, the results generated by sophisticated software like Altair CAE like Radios, OptiStruct, MotionSolve, AcuSolve (depending upon the type of analysis required these solutions can be used for structural analysis services, Product design optimization services, Kinematics and multibody dynamics services, thermal analysis services, computational fluid dynamics) is very accurate. Secondly, it saves enterprises time and money to test for vibration and noise by software rather than physically manufacturing a product. However, producing standardized tests which are equivalent to the product’s real-life vibration environment is often a great challenge. That is why it is necessary to use specialized noise and vibration analysis services. The cost of software is nothing to sneeze at. And it takes a great deal of experience to interpret the results properly and suggest a remedial solutions. Therefore, agencies that provide noise and vibration services are in demand. India, with technology at par with the rest of the world, is a hot favourite for rendering these services due to its highly skilled technicians and low cost.