Noise & Vibration studies are one of the most important aspects of designing any dynamic system. Any machinery which has components having high inertia, rotating components, friction, losses and other random forces create excitations at various locations for a system. Ducts are an excellent carrier of various types of vibrations which are created by these excitation forces and carry them to various locations nearby. Thus, if excessive noise levels are generated and transmitted to different ship locations, there are possibilities of detrimental effects such as hearing disabilities for crew and passengers onboard, failure of equipment’s due to resonance, noise emission to surroundings, violation of stealth requirements etc. This project focuses on primarily understanding the sources of noise & vibrations onboard marine vessels, transmission of these vibrations to various locations on ships via ducts and attenuation of the generated noise. Using the guidelines established by various classification societies such as American Bureau of Shipping, Bureau Veritas, Lloyd’s Register etc., a software package written in Python is developed to calculate the theoretical attenuation across the duct system for a case under consideration. A harmonic acoustic model is created in ANSYS software to replicate this noise & vibration scenario onboard ships for various duct subsystems. After the simulation is carried out, a comparison of the output of the Python package and ANSYS model is carried for attenuation of noise levels. This provides a basis for establishing the accuracy of the simulated model. It is found that the error is minimal and the 2 output results are in sync. Thus, this enables us to further improve these models for various ships and ensure the noise levels are restricted within the required limit"
1. HVAC system noise is a significant issue in ships, and current regulations lack specificity for equipment-generated noise.
2. Utilizes ANSYS software for creating a harmonic acoustic model, allowing for detailed analysis of various duct components.
3. Highlights the critical role of meshing in finite element analysis (FEA) for accurate simulations, discussing methods like tetrahedral and hexahedral elements.
4. Discusses the significance of realistic boundary conditions for obtaining meaningful simulation results in FEA.
5. Examines simulation results for straight ducts, turns, branches, plenums, and duct openings, comparing theoretical values with simulation outputs.
6. Acknowledges discrepancies between theoretical and simulated values, attributing them to software licensing limitations and meshing constraints.
7. Explores end reflection loss in duct openings and introduces the concept of silencers, highlighting the trade-off between pressure loss and low-frequency attenuation.
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“”Use of computer simulations in ANSYS software for sound propagation inside air ducts, providing advantages in terms of cost reduction and faster, accurate results compared to experiments.
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Research Intern, MRC